An evaporated fuel processing device may include: a canister; a purge passage through which purge gas sent from the canister to an intake passage passes; a pump; a control valve disposed on the purge passage and configured to switch between a communication state and a cutoff state; a specifying device configured to specify an evaporated fuel concentration of the purge gas in the purge passage when the purge gas is to be supplied from the canister to the intake passage. A controller may be configured to switch the control valve based on at least a first cycle and a second cycle which is longer than the first cycle. The specifying device may specify the evaporated fuel concentration of the purge gas in the purge passage while the pump is active and the control valve is in the cutoff state in the second cycle.