PURPOSE: To enable prevention of the generation of noise at a gear transmission device by a method wherein the edge part of an opening formed in a bracket for mounting a gear housing is bent inwardly, and the tip of the edge part is brought into contact with the side of a driven gear.

CONSTITUTION: During rotation of a motor 4, working noise is transmitted through an output shaft 5 to a recessed part 9a of a gear housing 9. Noise of engagement between a worm gear 6 and a work wheel 7 is generated at the housing recessed part 9a. However, since the tip of an edge part 21a of an opening 21b of a bracket 21 for mounting is brought into contact with the lower side of the wheel 7, the noise is confined at the interior of the recessed part 9a and is prevented from leakage to the outside. When a drive mechanism D is used for a long time, a slide part between the wheel 7 and a housing boss part 9b is worn and the wheel 7 generates vibration to generate secondary noise. However, since the lower side of the wheel 7 is guided by the tip of the edge part 21a of the opening 21b, the generation of vibration is suppressed to prevent the generation of noise.