To realize satisfactory steering feeling by changing a position of a break point of assist characteristic set by polygonal line function and suppressing the influence due to a load condition by simple processing.

An assist table 18a is expressed by polygonal line function. A compensation assist table 18b is prepared by changing the position of the break point of the polygonal line function. A microcomputer 12 determines a target current of an electric motor M in accordance with the compensation assist table 18b. The position of the break point is changed based on the results of detection of a load condition related to steering. The load condition can be detected by detecting changes of steering torque for a steering angle when steering is performed.