PURPOSE: To promote the yet thinner type of a reduction gear by extending a projection toward the outside of a motor end supporting a tuning shaft bearing, while threading an inner part of the projection, and attaching a reduction gear to it with a screw.

CONSTITUTION: Two projections 2, 3 are formed toward the outside from a motor end 1, and two screws 5, 6 for clamping a reduction gear 4 are screwed in the tapped holes. Each position of the projections 2, 3 is installable in making it get closer up to an outer circumference of the motor end 1 as there is no restriction from the standpoint of machining. Therefore each setup space of gears 14-17 becomes widened, thus the reduction gear 4 can be thinned as specified. In addition, each outer circumference of these projections 2, 3 is fitted in two locating holes 8, 9 bored in a lower surface 7 of the reduction gear 4, namely, serving as locating pins. In succession, positioning can be done without jumping out of a bearing 10, and a space necessary for an escape of this bearing 10 falls into disuse, so that a yet more thinner type of the reduction gear 4 is thus promotable.