A fuel cell system mounted in a vehicle includes a stack case for housing a fuel cell stack. In the stack case, a rear opening is formed in a rear portion facing backward. A cell voltage detection terminal electrically connected to an electrode of the fuel cell stack is exposed in the rear opening. A multilayer filter is provided in the rear opening. The multilayer filter has an inner mesh member, a filter member, and an outer mesh member. An electrical equipment housing case for housing electrical equipment faces the rear opening.