To provide a gear housing for a motor, capable of reducing a material and weight while increasing the rigidity of attachment leg parts.

A gear housing 11 for a motor is fixed to a motor main body rotating and driving a rotation axis, houses a worm and a worm wheel coupled with the rotation axis, and has three attachment leg parts 11d for fixing the gear housing to an attachment member, which are formed to protrude from one lateral face with an interval with one another. A swelling part 11e formed on an external side by swelling an interior space to be expanded is provided to the one lateral face of the gear housing 11. The swelling part 11e has a coupling wall part constituting a side wall part 11f of the swelling part 11e and standing from the one lateral face, and a swelling end wall part 11i constituting an upper wall part of the swelling part 11e and connecting standing direction front end sides of the coupling wall part. In addition, the three attachment leg parts 11d are coupled by the coupling wall part (the side wall part 11f) and the swelling end wall part 11i.