An evaporated fuel processing device may be provided with a canister configured to adsorb evaporated fuel evaporated in a fuel tank; a purge passage through which purge gas sent from the canister to the engine passes; a pump configured to send the purge gas from the canister to the intake passage; a control valve configured to switch between a communication state communicating the canister and the intake passage and a cutoff state cutting off the canister from the intake passage; a branch passage including one end connected to the purge passage on a downstream side relative to the pump and other end connected on an upstream side relative to the pump; and a concentration detector provided on the branch passage.