In a valve device for a fuel tank, a condition of blowing out a fuel to an outside of a fuel tank can be prevented as little as possible. The valve device includes a valve opening for communicating inside and outside of the fuel tank; a valve chamber formed below the valve opening; and a float disposed inside the valve chamber to be movable up and down, and the valve chamber has a structure of positioning an open end below a support portion of the float having a passage portion for a fluid. An orifice is formed in the support portion, and by a notch portion formed in the valve chamber, an entrance of an orifice-ventilation path communicating with the orifice is formed at a side lower than the support portion and at a side upper than the open end.