An electric power converting device can supply a constant voltage to a load while suppressing voltage variation in the AC power source, to reduce breakdown voltages of semiconductor switching elements. The device includes first to third switching element series circuits and at least a first capacitor connected in parallel. One end of the AC power source and one end of the load are connected to each other. Second and third capacitors are connected in parallel to the AC power source side and the load side, respectively. The one end of the power source is connected to a series connection point of the first switching element series circuit through a reactor, the other end of the power source is connected to a series connection point of the second switching element series circuit, and the other end of the load is connected to a series connection point of the third switching element series circuit through another reactor. Change in the power source voltage is compensated by a series converter, which is formed by the second and third switching element series circuits, and change in voltage of the capacitor due to the compensating operation is compensated by charging and discharging operation by a parallel converter formed by the first and second switching element series circuits.