A detecting device for solenoid operated valve, the valve being located between a pilot fluid pressure supply source via a pilot operated directional control valve associated with the solenoid operated valve and a drain tank and adapted to be switched over to either a connecting position where an inlet port thereof for pressurized pilot fluid is allowed to communicate with a drain port thereof connected to the drain tank or a disconnecting position where the inlet port is disconnected from the drain port. The detecting device has a cylinder chamber connected to the inlet port of the solenoid operated valve and a plunger inserted partially into the cylinder chamber so as to form a pressure chamber therebetween, wherein the plunger is able to be pushed manually into the pressure chamber only when the solenoid operated valve is kept at the connecting position.