diff --git a/engine/runtime/action-log/src/action.rs b/engine/runtime/action-log/src/action.rs
index cf9dfd921..19290603d 100644
--- a/engine/runtime/action-log/src/action.rs
+++ b/engine/runtime/action-log/src/action.rs
@@ -3,8 +3,7 @@ use std::path::PathBuf;
 use std::sync::Mutex;
 
 use once_cell::sync::Lazy;
-use slog::{Drain, Logger, OwnedKVList, Record};
-use slog_term::Decorator;
+use slog::Logger;
 use sloggers::file::FileLoggerBuilder;
 use sloggers::null::NullLoggerBuilder;
 use sloggers::types::Severity;
@@ -12,6 +11,8 @@ use sloggers::{Build, BuildWithCustomFormat};
 
 use reearth_flow_common::str::{is_boolean, parse_boolean};
 
+use crate::json::Json;
+
 static ACTION_LOG_DISABLE: Lazy<Mutex<Option<String>>> =
     Lazy::new(|| Mutex::new(env::var("ACTION_LOG_DISABLE").ok()));
 
@@ -22,84 +23,11 @@ pub(crate) fn action_logger(root_path: PathBuf, action: &str) -> Logger {
             NullLoggerBuilder.build().unwrap()
         }
         _ => {
-            let mut builder = FileLoggerBuilder::new(format!(
-                "{}/{}.log",
-                root_path.to_str().unwrap_or_default(),
-                action
-            ));
+            let mut builder = FileLoggerBuilder::new(root_path.join(format!("{}.log", action)));
             builder.level(Severity::Info);
             builder
-                .build_with_custom_format(|decorator| Ok(CustomFormat::new(decorator)))
+                .build_with_custom_format(|decorator| Ok(Json::new(decorator)))
                 .unwrap()
         }
     }
 }
-
-pub struct CustomFormat<D>
-where
-    D: Decorator,
-{
-    decorator: D,
-}
-
-impl<D> Drain for CustomFormat<D>
-where
-    D: Decorator,
-{
-    type Ok = ();
-    type Err = std::io::Error;
-
-    fn log(
-        &self,
-        record: &Record,
-        values: &OwnedKVList,
-    ) -> std::result::Result<Self::Ok, Self::Err> {
-        self.format_custom(record, values)
-    }
-}
-
-const TIMESTAMP_FORMAT: &[time::format_description::FormatItem] = time::macros::format_description!(
-    "[year]/[month]/[day] [hour]:[minute]:[second] [offset_hour]:[offset_minute]"
-);
-
-impl<D> CustomFormat<D>
-where
-    D: Decorator,
-{
-    pub fn new(decorator: D) -> Self {
-        CustomFormat { decorator }
-    }
-
-    fn format_custom(&self, record: &Record, values: &OwnedKVList) -> std::io::Result<()> {
-        self.decorator.with_record(record, values, |decorator| {
-            decorator.start_level()?;
-            write!(decorator, "[{:?}]", record.level())?;
-
-            decorator.start_whitespace()?;
-            write!(decorator, " ")?;
-
-            decorator.start_timestamp()?;
-            let now: time::OffsetDateTime = std::time::SystemTime::now().into();
-            write!(
-                decorator,
-                "{}",
-                now.format(TIMESTAMP_FORMAT)
-                    .map_err(|e| std::io::Error::new(std::io::ErrorKind::Other, e))?
-            )?;
-
-            decorator.start_whitespace()?;
-            write!(decorator, " ")?;
-
-            decorator.start_whitespace()?;
-            write!(decorator, " ")?;
-
-            decorator.start_msg()?;
-            write!(decorator, "{}", record.msg())?;
-
-            writeln!(decorator)?;
-            decorator.flush()?;
-
-            Ok(())
-        })
-    }
-}
diff --git a/engine/runtime/action-log/src/json.rs b/engine/runtime/action-log/src/json.rs
new file mode 100644
index 000000000..f0edca3e5
--- /dev/null
+++ b/engine/runtime/action-log/src/json.rs
@@ -0,0 +1,257 @@
+use serde::ser::SerializeMap;
+use serde::serde_if_integer128;
+use slog::o;
+use slog::Key;
+use slog::Record;
+use slog::{FnValue, PushFnValue};
+use slog::{OwnedKVList, SendSyncRefUnwindSafeKV, KV};
+use slog_term::Decorator;
+use std::{fmt, io, result};
+
+use std::cell::RefCell;
+use std::fmt::Write;
+
+thread_local! {
+    static TL_BUF: RefCell<String> = RefCell::new(String::with_capacity(128))
+}
+
+pub(crate) struct SerdeSerializer<S: serde::Serializer> {
+    /// Current state of map serializing: `serde::Serializer::MapState`
+    ser_map: S::SerializeMap,
+}
+
+impl<S: serde::Serializer> SerdeSerializer<S> {
+    /// Start serializing map of values
+    fn start(ser: S, len: Option<usize>) -> result::Result<Self, slog::Error> {
+        let ser_map = ser.serialize_map(len).map_err(|e| {
+            io::Error::new(
+                io::ErrorKind::Other,
+                format!("serde serialization error: {}", e),
+            )
+        })?;
+        Ok(SerdeSerializer { ser_map })
+    }
+
+    /// Finish serialization, and return the serializer
+    fn end(self) -> result::Result<S::Ok, S::Error> {
+        self.ser_map.end()
+    }
+}
+
+macro_rules! impl_m(
+    ($s:expr, $key:expr, $val:expr) => ({
+        let k_s:  &str = $key.as_ref();
+        $s.ser_map.serialize_entry(k_s, $val)
+             .map_err(|e| io::Error::new(io::ErrorKind::Other, format!("serde serialization error: {}", e)))?;
+        Ok(())
+    });
+);
+
+impl<S> slog::Serializer for SerdeSerializer<S>
+where
+    S: serde::Serializer,
+{
+    fn emit_bool(&mut self, key: Key, val: bool) -> slog::Result {
+        impl_m!(self, key, &val)
+    }
+
+    fn emit_unit(&mut self, key: Key) -> slog::Result {
+        impl_m!(self, key, &())
+    }
+
+    fn emit_char(&mut self, key: Key, val: char) -> slog::Result {
+        impl_m!(self, key, &val)
+    }
+
+    fn emit_none(&mut self, key: Key) -> slog::Result {
+        let val: Option<()> = None;
+        impl_m!(self, key, &val)
+    }
+    fn emit_u8(&mut self, key: Key, val: u8) -> slog::Result {
+        impl_m!(self, key, &val)
+    }
+    fn emit_i8(&mut self, key: Key, val: i8) -> slog::Result {
+        impl_m!(self, key, &val)
+    }
+    fn emit_u16(&mut self, key: Key, val: u16) -> slog::Result {
+        impl_m!(self, key, &val)
+    }
+    fn emit_i16(&mut self, key: Key, val: i16) -> slog::Result {
+        impl_m!(self, key, &val)
+    }
+    fn emit_usize(&mut self, key: Key, val: usize) -> slog::Result {
+        impl_m!(self, key, &val)
+    }
+    fn emit_isize(&mut self, key: Key, val: isize) -> slog::Result {
+        impl_m!(self, key, &val)
+    }
+    fn emit_u32(&mut self, key: Key, val: u32) -> slog::Result {
+        impl_m!(self, key, &val)
+    }
+    fn emit_i32(&mut self, key: Key, val: i32) -> slog::Result {
+        impl_m!(self, key, &val)
+    }
+    fn emit_f32(&mut self, key: Key, val: f32) -> slog::Result {
+        impl_m!(self, key, &val)
+    }
+    fn emit_u64(&mut self, key: Key, val: u64) -> slog::Result {
+        impl_m!(self, key, &val)
+    }
+    fn emit_i64(&mut self, key: Key, val: i64) -> slog::Result {
+        impl_m!(self, key, &val)
+    }
+    fn emit_f64(&mut self, key: Key, val: f64) -> slog::Result {
+        impl_m!(self, key, &val)
+    }
+    serde_if_integer128! {
+        fn emit_u128(&mut self, key: Key, val: u128) -> slog::Result {
+            impl_m!(self, key, &val)
+        }
+        fn emit_i128(&mut self, key: Key, val: i128) -> slog::Result {
+            impl_m!(self, key, &val)
+        }
+    }
+    fn emit_str(&mut self, key: Key, val: &str) -> slog::Result {
+        impl_m!(self, key, &val)
+    }
+    fn emit_arguments(&mut self, key: Key, val: &fmt::Arguments) -> slog::Result {
+        TL_BUF.with(|buf| {
+            let mut buf = buf.borrow_mut();
+
+            buf.write_fmt(*val).unwrap();
+
+            let res = { || impl_m!(self, key, &*buf) }();
+            buf.clear();
+            res
+        })
+    }
+}
+
+/// Json `Drain`
+///
+/// Each record will be printed as a Json map
+/// to a given `io`
+pub(crate) struct Json<D>
+where
+    D: Decorator,
+{
+    decorator: D,
+    values: Vec<OwnedKVList>,
+}
+
+impl<D> Json<D>
+where
+    D: Decorator,
+{
+    pub fn new(decorator: D) -> Json<D> {
+        JsonBuilder::new(decorator).add_default_keys().build()
+    }
+
+    fn log_impl<W, F>(
+        &self,
+        serializer: &mut serde_json::ser::Serializer<&mut W, F>,
+        rinfo: &Record,
+        logger_values: &OwnedKVList,
+    ) -> io::Result<()>
+    where
+        W: io::Write,
+        F: serde_json::ser::Formatter,
+    {
+        let mut serializer = SerdeSerializer::start(&mut *serializer, None)?;
+
+        for kv in &self.values {
+            kv.serialize(rinfo, &mut serializer)?;
+        }
+
+        logger_values.serialize(rinfo, &mut serializer)?;
+
+        rinfo.kv().serialize(rinfo, &mut serializer)?;
+
+        let res = serializer.end();
+
+        res.map_err(|e| io::Error::new(io::ErrorKind::Other, e))?;
+
+        Ok(())
+    }
+}
+
+impl<D> slog::Drain for Json<D>
+where
+    D: Decorator,
+{
+    type Ok = ();
+    type Err = io::Error;
+    fn log(&self, record: &Record, values: &OwnedKVList) -> io::Result<()> {
+        self.decorator.with_record(record, values, |decorator| {
+            let mut buffer = Vec::new();
+            let mut serializer = serde_json::Serializer::new(&mut buffer);
+            self.log_impl(&mut serializer, record, values)?;
+            serializer.into_inner();
+            let json_str = String::from_utf8(buffer).unwrap();
+            write!(decorator, "{}", json_str)?;
+            writeln!(decorator)?;
+            decorator.flush()?;
+            Ok(())
+        })
+    }
+}
+
+/// Json `Drain` builder
+///
+/// Create with `Json::new`.
+pub struct JsonBuilder<D: Decorator> {
+    values: Vec<OwnedKVList>,
+    decorator: D,
+}
+
+impl<D> JsonBuilder<D>
+where
+    D: Decorator,
+{
+    pub(crate) fn new(decorator: D) -> Self {
+        JsonBuilder {
+            values: vec![],
+            decorator,
+        }
+    }
+
+    /// Build `Json` `Drain`
+    ///
+    /// This consumes the builder.
+    pub fn build(self) -> Json<D> {
+        Json {
+            values: self.values,
+            decorator: self.decorator,
+        }
+    }
+
+    /// Add custom values to be printed with this formatter
+    pub fn add_key_value<T>(mut self, value: slog::OwnedKV<T>) -> Self
+    where
+        T: SendSyncRefUnwindSafeKV + 'static,
+    {
+        self.values.push(value.into());
+        self
+    }
+
+    /// Add default key-values:
+    ///
+    /// * `ts` - timestamp
+    /// * `level` - record logging level name
+    /// * `msg` - msg - formatted logging message
+    pub fn add_default_keys(self) -> Self {
+        self.add_key_value(o!(
+            "ts" => FnValue(move |_ : &Record| {
+                    time::OffsetDateTime::now_utc()
+                    .format(&time::format_description::well_known::Rfc3339)
+                    .ok()
+            }),
+            "level" => FnValue(move |rinfo : &Record| {
+                rinfo.level().as_short_str()
+            }),
+            "msg" => PushFnValue(move |record : &Record, ser| {
+                ser.emit(record.msg())
+            }),
+        ))
+    }
+}
diff --git a/engine/runtime/action-log/src/lib.rs b/engine/runtime/action-log/src/lib.rs
index 4b3766833..400df0a74 100644
--- a/engine/runtime/action-log/src/lib.rs
+++ b/engine/runtime/action-log/src/lib.rs
@@ -1,5 +1,6 @@
 mod action;
 pub mod factory;
+pub(crate) mod json;
 mod split;
 
 pub use slog::error as slog_error;