When a steering operation by a driver intervenes during autonomous driving of a vehicle, the intervention operation is fully reflected and a feeling of strangeness and a feeling of discomfort that may be given to the driver are reduced. In order to attain this, an ECU of an electric power steering apparatus includes: a steering angle control section 200 to which a steering angle command value is input to control a steering angle; an assist control section 147 to which an assist map gradual change gain is input to output an assist control output gradual change gain; and a switching determination/gradual change gain generating section 145 that generates a gradual change gain, by which steering angle control output and assist control output are multiplied, and multiplies the gradual change gain to make a switching determination between a steering angle control mode by the steering angle control section 200 and an assist control mode by the assist control section 147. The steering angle control section 200 has a position control section 208, a steering angular velocity control section 212, and steering intervention compensating and steering-wheel vibration suppressing means 220.