Inside a tank body storing a liquid, a return filter is provided protruding downward from an upper surface of the tank body, and a substantially plate-like (plate-shaped) float is also provided that is inserted into the tank body and floats in accordance with change in a liquid surface of the liquid stored in the tank body. The float is provided with an opening larger than a diameter of a filter case, and in a plan view, the float is disposed between the tank body and the filter case.