PURPOSE: To make a turn of a propulsion unit possible to do its regulation and release as leaving a steering handle gripped intact, by installing an operator for a steering lock in the vicinity of a grip of the steering handle being locked to the propulsion unit.

CONSTITUTION: When a grip 50 is held by the left hand, the thumb of the left and comes close to an operator 54 and each of levers 56 and 58 to that these part are operated by the thumb, through which control for speed and forward/ backward propulsion takes place. And, when the operator 54 is pushed toward the end of a handle 34 with the thumb, a pin 38 is pulled out of a long groove 36A of a plate spring 36 whereby regular steerage comes possible to be done. In the case where a propulsion unit is locked to a straight drive position, it will do that the operator 54 is slidden to the side of the grip 50 whereby the pin 38 engages the long groove 36A. Since an inclined plane is formed in both ends of the plate spring 36, even if the pin 38 is projected outward in a state that the propulsion unit is largely rolled and steered, the pin 38 rides on the inclined plane of the plate spring 36 which is therefore pushed downward so that the pin 38 engages the long groove 36A without the smallest strain. Thus, locking and releasing both are performable without using both hands.