If a main stop valve of a fuel gas tank is not opened, it becomes possible to display a remaining level of fuel gas. A remaining fuel level displaying method for the fuel cell system comprises: if the main stop valve is opened, then calculating a remaining level of fuel gas in the fuel gas tank using a pressure value acquired from the pressure sensor, and displaying the calculated remaining level of the fuel gas on a display device, and if the main stop valve is closed, then displaying on the display device a remaining level of the fuel gas that was stored into a memory at a time when the main stop valve was shut off.