A cooling system includes a compressor that circulates refrigerant; a condenser that condenses the refrigerant; an expansion valve that reduces a pressure of the refrigerant that has been condensed by the condenser; an evaporator that vaporizes the refrigerant that has been reduced in pressure by the expansion valve; a refrigerant passage through which the refrigerant flows from an outlet of the condenser toward an inlet of the expansion valve, and that includes a passage forming portion that forms part of the refrigerant passage; a second passage that is connected in parallel with the passage forming portion; a cooling portion that is provided in the second passage and cools a heat source using the refrigerant; and an expansion valve that is arranged upstream of the cooling portion in the second passage.
