An Assist Control Unit 61 detects a power generation state of an electric motor where the direction for generating torque of motor current im does not match the rotational direction of steering speed ωx (S12), and calculates an Amount E Corresponding to Power Generation Energy during a period when the power generation state is detected continuously (S15). When the Amount E Corresponding to Power Generation Energy exceeds a Criterion Value E0 (S16: Yes), the state is judged as a reverse input state that a large reverse input is acting on a steering mechanism from a tire. Consequently, a small reverse input state not affecting the steering mechanism is excluded, and a large reverse input state having a risk of affecting the steering mechanism can be detected precisely.
