The invention discloses an evaporated fuel processing device wherein, when fuel is being supplied and the internal pressure of a fuel tank is high, a shutoff valve is opened and evaporated fuel is made to flow to a canister through a path equipped with a float valve, thereby lowering the pressure in the fuel tank before a filling cap is opened. This evaporated fuel processing device is equipped with: a fill switch that is operated in order to direct that filling begin, and that issues a filling start signal; an internal pressure sensor that detects, as the internal pressure, the pressure of the space inside the fuel tank; and a shutoff valve control means that, when a filling start signal has been issued by the fill switch and the pressure inside the fuel tank as detected by the internal pressure sensor is higher than a preset pressure, causes the shutoff valve to open within a range wherein the float valve does not operate, and, from the time that the valve begins to open, increases the valve-opening speed of the shutoff valve in accordance with the decrease in the internal pressure of the fuel tank. By increasing the valve-opening speed of the shutoff valve in accordance with the reduction in the evaporated fuel so as to increase the flow volume of the evaporated fuel within a range wherein the float valve does not operate, the time required for the pressure in the fuel tank to decrease to the pressure at which filling is possible can be reduced.