A fuel cell system includes a fuel cell for causing electrochemical reactions of anode gas and cathode gas, a fuel cell system case accommodating the fuel cell, and a frame disposed below the fuel cell system case and fixing the fuel cell system case. A rib is provided on an upper surface of the frame. A water reservoir portion is provided in the bottom of the fuel cell system case so that the water reservoir portion is a concave in an inner side of the fuel cell system case and is a convex in the outside of the fuel cell system case. The water reservoir portion is located at a position at which at least a part of the convex vertically overlaps with the rib.