To reduce suction noises generated in outside air intake passages.

The outside air intake passages 29A, 29B are provided for taking outside air from the outside of a boat into an engine room in the boat, and suction resonators 42, 43 are mounted on the ways of the outside air intake passages 29A, 29B. The suction resonators 42, 43 are used for reducing suction noises generated in the outside air intake passages 29A, 29B.