Disclosed is a valve device for a fuel tank, which is provided with a float element which is contained within a case so as to move vertically, and is provided with a seal member on the top, said float element being moved upward by fuel introduced into the case through an inlet portion, to seat the seal member onto a vent valve port. A vent portion which links the inside of the tank and the inside of the case is formed on the top portion of the case, said top portion being positioned above the draft line of the float element when the seal member is seated, and the top portion of the float element, which is adjacent to the top portion of the case when the seal member is seated, reduces the amount of air passing through the vent portion. A restriction portion which maintains a constant gap between the top portion of the case and the top portion of the float element when the seal member is seated, is provided on the top portion of the case.