PURPOSE: To prevent the occurrence of defective operation during reversing by providing a stopper which engages with the peripheral edge parts of two gears, engaged with each other, only when they are positioned facing each other, to regulate rotation of a gear train, in a device which drives a valve body propeller shaft through a gear train with the aid of an electric motor.

CONSTITUTION: In a state that a stopper 41 of an intermediate gear 21b and a stopper 42 of a final gear 21c are brought into contact with each other, a valve body 15 located to the one end part of a propeller shaft 16 joined in a screwed-in state with the final gear 21c is brought into contact with a valve seat part 14 through the force of a spring 33 and forced into a closed state. When a first gear 21a is rotated counterclockwise with the aid of an electric motor 22, rotation is decelerated and transmitted through an intermediate gear 21b to a final gear 21c and converted into linear movement of the propeller shaft 16 by means of a screw joining part 27 to open the valve body 15. When the final gear 21c is rotated the given number of times, the inter gear 21b, a stopper 41, and the stopper 42 of the final gear 21c are brought into contact with each other again to stop rotation of the final gear 21c, and the valve body 15 is stopped in an full opening state.