Fuel cell system

A fuel cell system includes a fuel gas passage (6), a first gas supply source (60), a shutoff valve (69, 69f, 69s) provided at an upstream side relative to the first gas supply source at the fuel gas passage, a pressure detecting member (61) detecting a gas pressure (P1) of a passage portion (6m) of the fuel gas passage (6) between the shutoff valve and the first gas supply source, and a control portion (100). The control portion determines in a determination process whether or not the gas pressure decreases to or below a predetermined pressure (PA) after controlling the shutoff valve to be closed while driving the first gas supply source, and determines that a closing function of the shutoff valve is normal and an air tightness of the passage portion is normal in a case where the gas pressure decreases to or below the predetermined pressure.