To improve operability and workability when an engine is started in an engine hood open state for inspection/maintenance in an engine room.

A hood opening/closing detecting switch 9 turned ON/OFF associatively with the opening/closing of an engine hood is serially connected to the ignition switch 17 of an ignition circuit 16. A maintenance short-circuit connector 10 and a maintenance engine starting switch 11 set in a serial relation with each other are provided closed to each other in an engine room, and these are connected in parallel to the hood opening/closing detecting switch 9. If the engine is started in the open state of the engine hood, the maintenance engine starting switch 11 is pressed and operated after the maintenance short- circuit connector 10 is fitted and connected thereto.