A cooling system that cools a heat generating source mounted on a vehicle includes: a compressor that circulates refrigerant; a first heat exchanger that performs heat exchange between the refrigerant and outside air; a decompressor that decompresses the refrigerant; a second heat exchanger that performs heat exchange between the refrigerant and air-conditioning air; and a cooling device that is provided on a path of the refrigerant flowing between the first heat exchanger and the decompressor and that uses the refrigerant to cool the heat generating source. A capillarity generating portion that causes the refrigerant to rise due to capillarity is provided inside the cooling device.