To allow a water jet propelled boat to easily come alongside the pier by improving the turning performance of a body when inertially moved forward in the condition of an engine being stopped or idling.

The water jet propelled boat comprises sponsons 31, 32 desplaceably mounted on both sides of the body, a throttle opening detecting sensor 44 for detecting the throttle opening of the engine, and a steering angle detecting sensor 43 for detecting the steering angle and the direction of a steering handle 12. The sponson 31 (or 32) is controlled to be displaced by a hydraulic cylinder 331 so that the sponson 31 (or 32) corresponding to the steering direction is extended into water when the throttle opening of the engine is not larger than a set value and the steering angle is not smaller than a set value.