EVAPORATED FUEL PROCESSING DEVICE, PURGE GAS CONCENTRATION DETECTION METHOD, AND CONTROL DEVICE FOR EVAPORATED FUEL PROCESSING DEVICE

When a purge control valve is in a supply state of supplying purge gas from a canister to an intake pipe and a pump is in operation, a concentration detector is configured to detect a concentration of the purge gas when the purge control valve is open in a case where a duty cycle of the purge control valve is not less than a predetermined value, and detect a concentration of the purge gas when the purge control valve is closed in a case where the duty cycle of the purge control valve is less than the predetermined value.