This fuel cell system is provided with a first fuel-cell stack and a second fuel-cell stack having a lower output voltage than that of the first fuel-cell stack, a pre-switching stack consisting of the first fuel-cell stack or the second fuel-cell stack, a boosting stack consisting of the first fuel-cell stack or the second fuel-cell stack, and a post-switching stack consisting of at least the first fuel-cell stack, wherein, in a state in which the pre-switching stack and the load are connected, after boosting the voltage of the boosting stack, the fuel-cell system switches to a state in whichthe post-switching stack and the load are connected.