To properly absorb the impact energy of a primary collision and to reduce the damage to a driver caused by a secondary collision.

Each support part 6 for supporting a motor 5 for steering assistance on a stationary-side member is provided with a projecting part 11 projected at one end of a motor housing 51, and a recessed part 12 recessed in the stationary-side member for inserting the projecting part 11, and additionally provided with a movement permitting part 12b for permitting the relative movement of the projecting part 11 in the recessed part 12, and an evacuation part 13 for evacuating the projecting part 11 outward from the movement permitting part 12b. When the impact energy due to the primary or secondary collision is applied to the motor housing 51, the motor housing 51 is rotated, so that the support of the motor 5 on the stationary-side member can automatically be released.