A fuel cell system includes a control unit configured to perform air-conditioning-system preparation control, wherein, under the air-conditioning-system preparation control, when an air conditioning system is not requested to heat air, it is determined whether or not a coolant within a coolant circulation passage is capable of being supplied to an air conditioning circuit, when the coolant within the coolant circulation passage is not capable of being supplied to the air conditioning circuit, the heater is operated to maintain a first predetermined temperature or higher of the coolant within the air conditioning circuit, and when the coolant within the coolant circulation passage is capable of being supplied to the air conditioning circuit, the air-conditioning water pump is operated to draw the coolant from the coolant circulation passage into the air conditioning circuit and to maintain the first predetermined temperature or higher of the coolant within the air conditioning circuit.