A battery pack cooling system includes a plurality of cells disposed in an internal space of a battery pack case so as to form a cooling passage configured to cool the cell modules by cooling air flowing in the cooling passage. A first temperature sensor is a minimum temperature sensor disposed in the upstream position which becomes a lowest temperature. A second temperature sensor is a maximum temperature sensor disposed in the downstream position which becomes a highest temperature. A third temperature sensor is configured to measure the temperature of either the highest temperature or the lowest temperature disposed in a second cell module. A cooling passage includes a cooling air inlet passage, a cooling air exhaust passage, and a plurality of cooling branch passages disposed to connect the cooling air inlet passage and the cooling air exhaust passage in parallel.