A vaporized fuel processing apparatus has a canister capable of adsorbing vaporized fuel generated in a fuel tank, a vapor path connecting the canister to the fuel tank, a closing valve provided in the vapor path, a purge path connecting the canister to an intake path of an engine, a pressure sensor for detecting the inner pressure of the fuel tank, and an electric control unit controlling the vaporized fuel processing apparatus. When the inner pressure of the fuel tank is in excess of the measurement range of the pressure sensor, the learning of the valve opening start position is prohibited, and pre-learning depressurization control is performed through change of the stroke amount of the closing valve in the valve opening direction until the inner pressure of the fuel tank is within the measurement range of the pressure sensor.