A control device controls a power conversion circuit so as to adjust control values of a motor generator to optimum values. The power conversion circuit has switching elements for selectively connecting and disconnecting a battery and terminals of the motor generator. The control device sets a simulated voltage vector V(n+1) in one control-period forward to perform a prediction model control. On predicting a current, the control device uses a model in a rotary coordinate system, and sets the median value of the voltage vector V(n+1) in one control-period Tc to a value of the voltage vector V(n+1) in the rotary coordinate system. The control device sets, as the value of the voltage vector V(n+1) in the rotary coordinate system, the voltage vector V(n+1) when the half-time of the control-period Tc is elapsed from the time at the electric angle θ(n+1).