The electric power converter includes a series converter connected in series between an AC power supply 1 and a load 6, and having capacitors 30, 31 as a power supply for the converter, switching devices 12, 13, and diodes 16, 17; and a parallel converter connected in parallel to the AC power supply 1 and having the capacitors 30, 31, switching devices 10, 11, and diodes 14, 15. The series converter compensate the change in the voltage of the AC power supply 1 to feed a certain voltage to the load 6, and the parallel converter conducts charging and discharging operations to compensate the changes in the voltages of the capacitors 30 and 31 caused by the compensating operations of the series converter. The converter suppresses the change of the AC power supply voltage and feeds a certain voltage to the load at a high efficiency and low running costs.