To suppress vibration generated on an operation member and to enhance steering feeling.

A target current value is set based on steering torque T and vehicle speed V and an electric motor M is controlled by a proportional integration control part 30 such that the target current value is accomplished. Power of the electric motor M is transmitted to a steering mechanism 2 and steering assistance is performed. A vibration detection part 25 detects vibration of a steering wheel 1 based on the steering torque T. A continuation time when the vibration detection part 25 detects the vibration is measured by a continuation time measurement part 26. A gain setting part 27 variably sets the gain of the proportional integration control part 30 according to measurement result of the continuation time measurement part 26.