To provide an intake air cooling device for a small ship capable of suppressing rising of intake air temperature due to engine heat, and as a result, preventing deterioration of engine output due to deterioration of charging efficiency without causing a problem of securing installing space and a problem of an effect by water or the like entering a hull.

In a water vehicle (the small ship), an engine 10 is mounted in an engine compartment 2a inside the hull 2 formed substantially watertight and ducts 11 and 12 introducing external air to the engine 10 are inserted and arranged. In the intake air cooling device for the water vehicle, a cooler 45 comprised by forming a plurality of fins 45c on a cooler body 45a having a cooling water passage 45b is arranged near an upstream side of an inlet 25c of the engine 10, and a branched cooling water pipe 46 branched from a cooling water feed pipe 40 feeding engine cooling water to the cooling water passage 45b is connected to the cooler 45.