Fuel cell system

A fuel cell system includes a control portion. (100) which airtightly closes a passage portion (6m) provided on a fuel gas passage (6) between a shut-off valve (69, 69f, 69s) and an opening-and-closing valve (66) by closing the shut-off valve (69, 69f, 69s) and the opening-and-closing valve (66) in a state where a fuel gas from a gas source (63) is supplied to the fuel gas passage (6) by opening the shut-off valve (69, 69f, 69s) and the opening-and-closing valve (66). Thereafter, the control portion (100) performs a determination processing for determining whether a closing function of the shut-off valve (69, 69f, 69s), a closing function of the opening-and-closing valve (66), and an airtightness of the passage portion (6m) function as normal on the basis of an elapsed time elapsed from a reference timing related to the closing of the both of the shut-off valve (69, 69f, 69s) and the opening-and-closing valve (66) and a fluctuation of the pressure detected by the pressure detection element in a state where the first gas conveying source (60) is stopped.