Disclosed is an evaporated fuel processing apparatus for an internal combustion engine including: a canister; and a purge passage supplying purge gas including evaporated fuel separated from the canister to an intake system therethrough; characterized in that the evaporated fuel processing apparatus further comprises a pulsation pump supplying the purge gas to the intake system by using a pumping action responding to intake pulsation generated in an intake passage of the internal combustion engine. The pulsation pump includes: a first chamber; a communication passage communicating with the first chamber and the intake passage; an elastic body being deformed depending on pressure fluctuation of the first chamber; a second chamber formed so as to surround the elastic body; a suction port provided with a check valve allowing inflow of gas into the second chamber, and a discharge port provided with a check valve allowing outflow of gas from the second chamber.