PURPOSE: To improve the operational performance against the spring-up of a propulsion unit at the time of beach-landing by providing the captioned motor with a first and a second connecting passages of a cylinder, a closing valve for the connecting passage, and a remote control part for this closing valve.

CONSTITUTION: A connecting passage 71, which connects the upper chamber and the lower chamber of a cylinder 18, connects the upper chamber to the lower chamber in a direct and short-circuit manner. Therefore, the passage 71 can be short and free from sharp or many curves. As a result, passage resistance, which acts on the working oil that moves between the upper chamber and the lower chamber of the cylinder at the time of beach-landing, becomes small, and, at the same time, the spring-up resistance due to this passage resistance becomes small as well. Accordingly, the spring-up responsiveness at the time of beach-landing can be improved. In addition, even if the beach-landing is repeated frequently, less damage will be done to the outboard motor, and the operational performance against the spring-up can be improved.