A cooling device includes: an air blast passage; a heater core that is disposed in the air blast passage; an air blast volume adjusting member that is opened and closed to adjust an air blast volume which flows in the heater core; a flow rate adjuster that adjusts a flow rate of the coolant which is introduced into the heater core; and a controller. The controller sets the flow rate of the coolant which is adjusted by the flow rate adjuster to be less than a lower limit value of an adjustable range of the flow rate of the coolant which is adjusted by the flow rate adjuster in a vehicle compartment air-conditioning state in which the air blast volume adjusting member allows an air blast to flow to the heater core when the air blast volume adjusting member fully closes the heater core side of the air blast passage.