It is an object to effectively reduce minute clearances generated between a heat radiating member and a vehicle body and ensure good cooling performance while avoiding the occurrence of impact and noise caused by the vibration of a vehicle. A circuit unit U is mounted such that an outer surface 11B of the heat radiating member 10 to which the circuit body 30 is fixed faces a body surface S of the vehicle with a clearance. Preferably, the mounting part 12 fixed to the body of the vehicle is extended, the surface 13 of the mounting part 12 which is in contact with the body is positioned to be substantially parallel to the outer surface 11B of the heat radiating member and a step is provided in both surfaces 13, 11B. In a mounted state, the body and the outer surface 11B of the heat radiating member are facing each other in a substantially parallel state and a clearance is formed between the body and the outer surface of the heat radiating member over the entire area excluding the mounting part 12.