A driving-side transmission portion of an output shaft of an electric motor and a driven-side transmission portion of a worm shaft are coupled to each other via a torque transmission joint including an elastic member and a coupling such that the torque can be transmitted. One axial end portion of a coupling-side concave-convex portion of the coupling is engaged with a first driving-side concave-convex portion of the driving-side transmission portion with a gap in the circumferential direction, and the other axial end portion thereof is engaged with a first driven-side concave-convex portion of the driven-side transmission portion with a gap in the circumferential direction. The elastic member is provided between an axial center portion of the coupling-side concave-convex portion, and a second driving-side concave-convex portion of the driving-side transmission portion and a second driven-side concave-convex portion of the driven-side transmission portion such that the torque can be transmitted respectively.