PURPOSE: To permit change of the pitch of vanes on a fan or a pump by clockwise or counterclockwise rotating a reversible motor to shift a slide element with a nut, thereby moving a disc-like working plate left and right.

CONSTITUTION: When a switch 23 of a reversible motor 12 is acutated, a screw 14 is rotated left or right to move a slide element 15 with a nut left or right. Accompanied with this, a pusk plate 10 is shifted to the left or the right by the medium of a push rod 18 so that an angle between vanes 1 can be changed. Since rotation of a working plate 4 will not cause any rotation of the pusk plate 10, the change of angle may be carried out even in operation. In this device, since the force for changing the angle of the vanes is enhanced with the aid of a deceleration gear 13 and the screw 14, the reversible pump 12 may reduced in size and since the screw 14 provides a self-locking effect, the vanes can be fixed under a high power even in the absence of electric current.