PURPOSE: To detect the rotation accurately and to realize the simplification of component parts and the compact size of product by making a same rotary body have the functions of a disk for detecting rotation and a rotary electrode in an ignition distributor concurrently, in an angle detecting device for internal combustion engine.

CONSTITUTION: The shaft 50 of an ignition distributor 38 for an internal combustion engine is contacted to the rotary shaft of the engine through a coupling 51, and held by a bearing 52. In this case, a rotary electrode 1 for distributing ignition is provided to the shaft 50 so as to distribute the ignition from a central electrode 54 to a side electrode 55. And a rotary disk 2 for angle detecting is provided to the rotary electrode 1. Furthermore, an optical film cable 15 is held by a receptacle 20 and a sensor head connector 10 installed to a housing 56, to oppose to the rotary disk 2. Light is projected to the reflection plate of the rotary disk 2 from the optical fiber cable 15, and its reflection light is irradiated to a rotation detecting module (rotation angle detecting device) 60.