A cooling system is provided. The cooling system includes: a fuel cell; a cooling circuit configured to circulate a coolant medium to cool the fuel cell; an air conditioning circuit configured to circulate the coolant medium, the air conditioning circuit having a heat exchanger to execute heat exchange between the coolant medium and air to be sent to a room; a switching unit configured to switch between a connected state and a disconnected state; and a controller configured to control operation of the cooling system, wherein when the controller switches a state of the cooling system from the disconnected state to the connected state, irrespective of conditions in the cooling system, the controller executes operation of the cooling system in a flow rate control mode whereby the ratio (L1/L2) of a first flow rate (L1) to a second flow rate (L2) is set to or above a prescribed value, wherein the first flow rate (L1) represents the flow rate of the coolant medium flowing through the cooling circuit, and the second flow rate (L2) represents the flow rate of the coolant medium flowing through the air conditioning circuit.