There is provided a valve device, including: a housing in which, via a partition wall, a valve chamber is provided below the partition wall and a vent chamber is provided above the partition wall, and a vent hole through which the valve chamber and the vent chamber communicate with each other is provided in the partition wall; and a float valve. A valve seat is formed on a side of the valve chamber of the partition wall, and an opening is provided on an inner side of the valve seat. The opening includes a first opening and a second opening extending outward in a slit shape from an outer periphery of the first opening. A seal part having elasticity that contacts with and separates from the valve seat to close and open the first opening and the second opening, is disposed above the float valve.