An electric motor is driven with high output at the time of low-speed running, and a steering at a high resolution is enabled at the time of fast-speed running. An electric power steering device causes the electric motor to generate auxiliary torque in accordance with the largeness of steering wheel torque by the steering operation of a wheel made by a driver and reduces the steering wheel torque to the driver. A control device drives, based on a vehicle-speed signal (Vs) from a speed sensor, the electric motor with high output at the time of low-speed running, and enables steering at a high resolution at the time of fast-speed running without increasing an electric-motor output.