This cathode-side humidification tank 1038 also functions as a coolant tank. The water in the cathode-side humidification tank 1038 cools the fuel cell 1030 and returns to the cathode-side humidification tank 1038. In the foregoing situations where the fuel cell 1030 is low in temperature, such as during the startup of the fuel cell system 1100, the coolant warmed by the heat exchanger HEX05 can also be supplied to the fuel cell 1030 to warm up the fuel cell 1030. Moreover, a coolant channel 1040 for supplying a coolant to a cooling plate 1036 provided in the fuel cell 1030 is in connection with a heat exchanger HEX06 which is formed in an anode-side humidification tank 1042. Consequently, the coolant even plays the role of maintaining the cathode-side humidification tank 1038 and the anode-side humidification tank 1042 in almost the same temperatures.