PURPOSE: To make variable the pitch of a propeller without using any hydraulic servo mechanism, by a method wherein a feed screw body for reciprocating a crank mechanism for changing blade pitch is engaged with and disengaged from a propeller shaft and is rotated forwardly and reversely.

CONSTITUTION: A feed screw body 14 is provided in the interior of the propeller shaft 5, and is prevented from rotating by a stopper 39 provided on a casing 1. A threaded part 14c of the feed screw body 14 is engaged with a female screw body 23, which is rotated forwardly or reversely by the propeller shaft 5 through an engaging and disengaging mechanism 21 or 22. The displacement quantity of the feed screw body 14 is detected by a detector 34. Accordingly, a variable- pitch propeller can be constituted without using any hydraulic servo mechanism, and cost can be reduced.