An evaporated fuel processing device may include a canister retaining evaporated fuel in a fuel tank, a vent passage communicating the canister and an intake passage of an engine, a first pump that discharges mixed gas of air and the evaporated fuel to the intake passage via the vent passage, a detector that detects a first pressure value indicating a pressure of the mixed gas discharged by the first pump, a memory storing pressure value-concentration correlated data indicating mixed gas, an acquisition unit that acquires a third pressure value indicating an air pressure detected by the detector in a case where the air containing substantially no evaporated fuel is discharged by the first pump, and an estimation unit that estimates a concentration of the evaporated fuel contained in the mixed gas discharged by the first pump by using the first and third pressure values and the pressure value-concentration correlated data.