PURPOSE: To enable to perform the on-off operation of a hatch cover so easily on the surface of the water by attaching the hatch cover and a steering pole rotatably to the same shaft in substance at their front ends, while installing an engaged means which engages both of them with each other.

CONSTITUTION: A jet propulsion boat hull 1 is composed of joining a deck member 11 and a boat bottom plate 12 with each other at their peripheral edges, and its seat 3 is installed on a seat base 13 installed in a central part in the width direction at the rear side from the hull central part. In addition, at the central part of a closable hatch cover 6 covering the upside of an engine room is installed at a front side of the seat 3. In this case, this hatch cover 6 is installed rotatably around a shaft 40 via a bracket 61 installed in the front side, while a base end 55 of a steering pole 5 is installed rotatably around this shaft 40. Thus, the hatch cover 6 is made maintainable in an opened state by means of a stopper means consisting of a lock pin 7 being fitted in engaged holes 71, 72.