This intake air cooling device is equipped with: a first radiator (13) that causes heat to be exchanged between a cooling fluid flowing out from an engine (11) and the outside air; a second radiator (14) that causes heat to be exchanged between the cooling fluid that has been cooled by the first radiator (13) and the outside air; a first intercooler (15) that causes heat to be exchanged between the cooling fluid that has been cooled by the second radiator (14) and intake air to the engine (11), thereby cooling the intake air; a second intercooler (16) that causes heat to be exchanged between the cooling fluid flowing out from the engine (11) and the intake air to the engine (11), thereby cooling the intake air; a branching section (23) that causes the flow of the cooling fluid flowing out from the engine (11) to split into a first radiator-side flow (FR) toward the first radiator (13) and a second intercooler-side flow (FI) toward the second intercooler (16); and a switching section (17) that blocks or allows the first radiator-side flow (FR) to circulate.