CONTROL DEVICE FOR FUEL VAPOR TREATMENT APPARATUS

The fuel vapor treatment apparatus includes a fuel tank, a canister, a vapor passage, a purge passage, a sealing valve, a purge valve, an outside air introduction passage, a switching valve, and a differential pressure detector. A processing device of the fuel vapor treatment apparatus includes a purge control unit and a purge diagnosis unit. The purge control unit performs a purge process by opening the purge valve in a state where the purge valve and the sealing valve are closed and the switching valve is opened. The purge diagnosis unit diagnoses whether or not the purge process is normal based on the amount of change in the differential pressure between before and after the opening of the purge valve.