In a power converter which performs power conversion between plural-phase AC and DC, variation in voltage of the DC capacitor in each converter cell is detected, and when the variation exceeds a predetermined value, a DC voltage command value as a control target value in a DC voltage control unit which controls DC voltage between DC buses is corrected by being increased or decreased. Thus, when AC grid failure occurs, the capacitor voltage of each converter cell is maintained and the operation continuity is improved.