diff --git a/README.md b/README.md
index 080aa97..1dc6742 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,42 @@
-# delivery_reservation_lamp_manager
+# Lamp manager for delivery reservation
+
+## Overview
+By changing lighting pattern of the lamp, this node notifies surrounding workers of on-demand delivery reservation status through `/dio_ros_driver`. 
+
+Lighting patterns are listed below.
+<table>
+  <thead>
+    <tr>
+      <th scope="col">Reservation status</th>
+	    <th scope="col">lighting pattern</th>
+	  </tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td>Not reserved</td>
+      <td>Off</td>
+    </tr>
+    <tr>
+      <td>In progress</td>
+      <td>Blinks</td>
+    </tr>
+    <tr>
+      <td>Reserved</td>
+      <td>Light up</td>
+    </tr>
+  </tbody>
+</table>
+
+## Input and Output
+- input
+  - from [autoware_state_machine](https://github.com/eve-autonomy/autoware_state_machine)
+    - `/autoware_state_machine/lock_state` : Reservation status for on-demand delivery.
+- output
+  - to [dio_ros_driver](https://github.com/tier4/dio_ros_driver)
+    - `/dio/dout3` : Digital-out assignment to a 3rd pin in [0-7] general-purpose outputs. This topic is remapped from `/delivery_reservation_lamp_out`.
+
+## Node Graph
+![node graph](http://www.plantuml.com/plantuml/proxy?src=https://raw.githubusercontent.com/eve-autonomy/delivery_reservation_lamp_manager/docs/node_graph.pu)
+
+## Parameter description
+This node has no parameters.
diff --git a/docs/node_graph.pu b/docs/node_graph.pu
new file mode 100644
index 0000000..48f0b45
--- /dev/null
+++ b/docs/node_graph.pu
@@ -0,0 +1,11 @@
+@startuml
+
+usecase "/autoware_state_machine"
+usecase "/delivery_reservation_lamp_manager" #LightCoral
+usecase "/dio_ros_driver"
+
+(/autoware_state_machine) -> (/delivery_reservation_lamp_manager) : /autoware_state_machine/lock_state
+
+(/delivery_reservation_lamp_manager) -> (/dio_ros_driver) : /dio/dout3
+
+@enduml