A fuel cell system including a fuel cell, includes: a heater core used by a heating device; a first circulation circuit arranged to circulate a heat medium through the fuel cell; a second circulation circuit arranged to circulate the heat medium through the heater core; a connection channel arranged to connect the first circulation circuit with the second circulation circuit and thereby circulate the heat medium between the first circulation circuit and the second circulation circuit; and a first temperature regulator located on the second circulation circuit and downstream of the heater core and configured to regulate temperature of the heat medium after flowing out of the heater core and before flowing into the fuel cell.