A fuel cell system (10) includes a fuel cell stack (12), a cathode supply path (62), a cathode discharge path (64), a cathode bypass path (66), and a controller (911). The cathode supply path (62) supplies a cathode gas to the fuel cell stack (12), and the cathode discharge path (64) discharges a cathode off-gas. The cathode bypass path (66) connects the cathode supply (62) and the cathode discharge path (64). During first power generation while the fuel cell stack (12) generates electric power at a warm-up time, the controller (911) controls a first valve (74) and a third valve (78) to be open, and an opening degree of a second valve (76) to be closer to a closed side than during second power generation when and after the warm-up is completed.
