PURPOSE: To very easily execute a change of a manual hydraulic steering system steering device with a cable steering system steering device.

CONSTITUTION: A steering cylinder unit 13 is set up in a swivel bracket 16 for supporting a propulsive unit to a ship body, a piston rod 26 of the steering cylinder unit is connected to a steering arm 18 for making the propulsive unit steerable, and an operating oil switching unit 19 for switching a flow of operating oil, supplied to this steering cylinder unit, is connected to the steering cylinder unit. In a ship propeller steering device for switching a flow of operating oil, supplied to the steering cylinder unit, by sliding a spool valve 31 of the operating oil switching unit by actuating a manual hydraulic cylinder device 40 actuated by operating an operating handle set up in the ship body, the manual hydraulic cylinder device is removably mounted on the steering cylinder unit.