To provide an electric power steering apparatus in which it is possible to reduce a size of the entire structure of a control unit while sufficiently showing a heat radiation effect of heat generating members. The electric power steering apparatus includes a steering column 3 having inserted therein a steering shaft 2 to which steering torque is transmitted, a reduction gear box 4 coupled to the steering shaft 2, and an electric motor 5 that transmits a steering assisting force to the steering shaft 2 via a reduction mechanism in the reduction gear box. In the reduction gear box 4, a motor mounting section 17 for mounting the electric motor 5 is formed at an end face in a direction perpendicular to an axis of the steering shaft 2 and a control-unit mounting section 20 for mounting a control unit 19 for controlling to drive the electric motor 5 is formed near the motor mounting section 17.