A valve device includes a float and a case storing the float. The valve device forms a part of a ventilation passage of a fuel tank. The case includes a partition wall which divides inside the case into an upper chamber and a storage chamber to house the float. The partition wall includes a rising portion opened and closed by the float, and a rising portion which surrounds the opening in the upper chamber. A dividing portion is formed in the rising portion to guide liquid to flow downward, and an upper surface of the partition wall outside the rising portion is formed with a gradient such that a side of the dividing part is a low part of an inclined portion thereof.