Under a low load condition, a produced torque is small and a synthetic current command I* with respect to an armature of a servomotor is small so that a magnitude in a negative direction of a reactive current command Id* determined by Id*=−|I*|·sin θ is small. As a result, under the low load condition, the synthetic current flowing through the armature can be small, and generation of wasteful heat can be suppressed. Further, under a high load condition, because a q-axis current Iq that produces the torque is large, voltage saturation is liable to occur. However, at the same time, the overall current command I* is large under the high load condition, and Id* is large in the negative direction. Therefore, a large reactive current Id can be flowed in the negative direction, and voltage saturation under the high load condition can be effectively prevented.