A valve device for a fuel tank, comprising: a first valve opening for communicating inside and outside of a fuel tank; a first valve chamber formed below the first valve opening; a notch portion formed in the valve chamber; a first float disposed inside the first valve chamber to be movable up and down; and a support portion for the first float having a passage portion for a fluid, and an orifice; wherein the valve chamber has an open end below the support portion, said valve device being characterized in that when the fuel level inside the fuel tank reaches the open end of the first valve chamber, a rise of an internal pressure of the fuel tank, and an inflow of the fuel into the first valve chamber accompanied by the rise of the internal pressure of the fuel tank can be made, so that the first float rises to close the first valve opening, and by the rise of the internal pressure of the fuel tank, the fuel level inside a filler pipe rises, and a sensor of a fuel feed gun detects filling-up fuel feed so as to stop fuel feed, in a side portion of a second valve chamber and above a second support portion, there is formed a ventilation window hole, and after the fuel feed stops, the ventilation is carried out mainly through the ventilation window hole and a second valve opening, and the first valve chamber includes an orifice and an orifice-ventilation path, and an entrance of the orifice-ventilation path is positioned at a side lower than the support portion and at a side upper than the open end of the first valve chamber by notch portions formed in the open end of the first valve chamber so as to allow the additional fuel feed until the fuel liquid level inside the fuel tank reaches the entrance of the orifice-ventilation path. a first valve opening for communicating inside and outside of a fuel tank; a first valve chamber formed below the first valve opening; a notch portion formed in the valve chamber; a first float disposed inside the first valve chamber to be movable up and down; and a support portion for the first float having a passage portion for a fluid, and an orifice; wherein the valve chamber has an open end below the support portion, said valve device being characterized in that when the fuel level inside the fuel tank reaches the open end of the first valve chamber, a rise of an internal pressure of the fuel tank, and an inflow of the fuel into the first valve chamber accompanied by the rise of the internal pressure of the fuel tank can be made, so that the first float rises to close the first valve opening, and by the rise of the internal pressure of the fuel tank, the fuel level inside a filler pipe rises, and a sensor of a fuel feed gun detects filling-up fuel feed so as to stop fuel feed, in a side portion of a second valve chamber and above a second support portion, there is formed a ventilation window hole, and after the fuel feed stops, the ventilation is carried out mainly through the ventilation window hole and a second valve opening, and the first valve chamber includes an orifice and an orifice-ventilation path, and an entrance of the orifice-ventilation path is positioned at a side lower than the support portion and at a side upper than the open end of the first valve chamber by notch portions formed in the open end of the first valve chamber so as to allow the additional fuel feed until the fuel liquid level inside the fuel tank reaches the entrance of the orifice-ventilation path.