A fuel tank valve device includes a housing in which a partition wall defines a lower valve chamber and an upper ventilation chamber, and a first opening and a second opening are provided to establish a communication between the lower valve chamber and the upper ventilation chamber, a first float valve that is accommodated in a first valve chamber of the lower valve chamber so as to rise and fall and that closes the first opening when a fuel level in a fuel tank nearly reaches a set full fuel level, and a second float valve that is accommodated in a second valve chamber of the lower valve chamber so as to rise and fall and that closes the second opening when the fuel level in the fuel tank rises abnormally.