A fuel cell system includes: a fuel cell; a normally-closed first shut-off valve provided upstream from the fuel cell and opening and closing pipes c1 and allowing air supplied from an air pump to pass therethrough; a normally-closed second shut-off valve opening and closing a pipe allowing cathode off-gas, discharged from the fuel cell, to pass therethrough; a valve-driving section for opening and closing discs of the shut-off valves; and valve lock units maintaining discs of the shut-off valves in open state when the cathode is released by opening the first shut-off valve and the second shut-off valve during electro-chemical reaction progressing in the fuel cell. This structure provides a simple and small-size fuel cell system capable of maintaining opening state of shut-off valves stably and reliably.