An evaporated fuel treatment device is provided to treat evaporated fuel by using a fuel supply cap with a small size while the flowout of fuel can also be suitably prevented. The evaporated fuel treatment device includes a positive pressure adjusting valve which opens when an inner pressure of a fuel tank becomes a predetermined pressure or more, and a spherical rollover valve which closes the positive pressure adjusting valve when the fuel tank is inclined at an angle equal to or larger than a predetermined angle. The positive pressure adjusting valve and the spherical rollover valve are mounted on one cylindrical portion formed on a fuel supply cap.