To control or adjust a boat with one manual lever by providing one manual lever to be turned within an operation guide flat surface or a control guide flat surface, and increasing or decreasing the blade pitch within the turning area with increase of the turning angle of the manual lever so as to increase the number of revolution of a motor.

A turning shaft 2 is supported by a casing 1 of a manual lever control device, and a manual lever 5 is supported by the turning shaft 2 freely to be turned around a shaft 4 vertical to an axis 3 of the turning shaft 2. The manual lever 5 is passed through a casing cover 6, and extended through a switching passage formed in the casing cover. The turning shaft 2 is connected to a potentiometer 10, and the potentiometer belongs to a device for changing the blade pitch of a variable pitch propeller. The turning shaft 2 is connected to a motor control device for motor. With this structure, a boat operator can securely control each function of the variable propeller and a clutch.