A fuel supply system includes a fuel gas tank; a temperature detecting portion; a fuel gas discharge flow path; a main stop valve that is provided in the fuel gas discharge flow path; and a control portion. The main stop valve includes an inlet portion and an outlet portion, a main valve that is arranged between the inlet portion and the outlet portion and that opens and closes the fuel gas discharge flow path, a pilot flow path that is provided so as to communicate the inlet portion with the outlet portion, a pilot valve that opens and closes the pilot flow path, and an actuator capable of opening and closing the main valve and the pilot valve at different timings. The control portion opens the pilot valve and closes the main valve when the detected temperature is equal to or lower than a first reference temperature.