A battery cooling system includes a cooling water circulation circuit for circulating cooling water for cooling the battery, a first heat exchanger for exchanging heat between air and cooling water, a second heat exchanger for exchanging heat between the low-pressure refrigerant of the refrigeration cycle circuit and cooling water, and an ion exchanger for removing impurity ions contained in the cooling water. The first heat exchanger and the second heat exchanger are arranged in series in the cooling water circulation circuit. The ion exchanger is disposed on the downstream side of the second heat exchanger in the cooling water circulation circuit.