To provide an intake air cooling device stably performing intake air cooling required for keeping high combustion efficiency of an engine while dispensing with complicated estimation, control, etc.

The intake air cooling device 10 integrally includes a cooling part 13C cooling the intake air supplied to the onboard engine, and a bypass path 15 internally bypassing the cooling part 13C. The inlet of the bypass path 15 includes a pressure shut-off valve 20 which naturally opens upon application of a predetermined pressure corresponding to the pressure of the intake air detoured to the bypass path 15 side by freezing at the cooling part 13C.