A fuel cell system includes a fuel cell stack and a mounting section. The fuel cell stack is mounted on the mounting section with inclination. The fuel cell stack is formed by stacking a plurality of fuel cells in a vertical direction. An oxygen-containing gas in an oxygen-containing gas flow field and a fuel gas in a fuel gas flow field flow in a counterflow manner. In a front box of a vehicle, an inlet side of the fuel gas flow field is positioned above an outlet side of the fuel gas flow field with respect to a horizontal direction. In this state, the fuel cell stack is mounted on the mounting section. The fuel cell stack is inclined downward from the horizontal direction toward the back of the vehicle in a vehicle length direction.