To appropriately balance operation responsiveness and operation stability of an electric motor in a normal steering operation, and to operate the electric motor at high responsiveness in an extremely sudden steering operation.

When a steering sudden operation is performed so that the difference between a basic target rotation speed Ra set by a basic target rotation speed setting section 32 and a motor rotation speed R calculated by a motor rotation speed calculating section 33 is larger than a predetermined speed difference D, a target rotation speed changing amount α according to the difference is set by a setting section 34 of the target rotation speed changing amount, and a value derived by adding the target rotation speed changing amount α to the basic target rotation speed Ra is set at a target rotation speed of the electric motor. The target rotation speed changing amount α is set to monotonically increase from zero with respect to the difference increase in a range where the difference between the basic target rotation speed Ra and the motor rotation speed R is larger than the speed difference D.