PURPOSE: To improve safety and operability by providing a lock means preventing the opening of a cover member and a means detecting the travelable state of a vehicle, and locking the cover member when the travelable state of the vehicle is detected.

CONSTITUTION: A metal cover member is openably fitted to the dust box opening section of a floor cleaning vehicle. An electromagnet 20 having a square shape is fixed to the periphery of the opening section, and it is connected to a power source 22 via a selector switch 21. An ignition switch IG starting or stopping an engine 23 is provided. When the engine 23 is started via the ignition switch IG to make the vehicle travelable, the selector switch 21 is turned on via a circuit, and the cover is attracted and locked by the electromagnet 20. The opening of the cover during a travel is surely prevented, the cover is easily opened or closed, and the deformation of the cover caused by a forced mechanical lock can be prevented.