To provide a gear housing comprising a front housing having a structure which can make the front housing lightweight and which can increase the strength of a continuous section of a worm wheel housing portion and a support portion where stress tends to be concentrated. A front-side housing is made of synthetic resin, and includes a housing front plate portion which constitutes a worm wheel housing portion and a support portion integrated with the housing front plate portion. A reinforcing member made of a metal plate is provided at a corner portion between a front surface of the housing front plate portion and a lower surface of the support portion.