To provide a backlash adjusting mechanism of a worm gear which does not necessitate an area beyond necessity and can adjust rickety motion properly and stably.

In a worm gear consisting of a worm 11 and a worm wheel 10, a first mounting member 1 mounted on the worm wheel 10, a second mounting member 2 which is mounted on the worm 11 and is formed in such a manner that it can slide in the orthogonal direction to the worm 11, and a lever 3 which performs the slide operation with the first mounting member 1 are provided, a projection part 1a having a parallel part which is parallel with the direction of slide in a section where the first mounting member 1 is mounted on the worm wheel 10 is formed, and a cutout part 2a is formed in the second mounting member 2 in such a manner that it is fitted in the parallel part of the projection part and slides.