To provide a small vessel seat device capable of stable holding a crew during traveling.

Foot placing sections 4b are formed in both sides of a substantially watertight hull 2 in a ship width direction and, when a seat device is to be constituted for a water vehicle (small vessel) provide in thelongitudinal direction of the hull with straddle seats 9 for seating a plurality of crews disposed in an upper surface central part, a roughly U-shaped grip is formed to be composed of a backrest section 62 between the upper end parts of a pair of arm sections 61 and 61, the lower end part of each arm section 61 is journaled by supporting members 70 loaded in both side walls of the hull 2 in a ship width direction and the backrest section 62 is swung formed in back and forth directions of the hull in the upper side of the seat.