A power conversion device has single-phase sub-inverters (2a) to (2c), each connected in series with respective phase of a three-phase main inverter (1) having a smoothing capacitor (6), which is fed from a power supply (11) via a converter (5), as a DC input thereof, and feeds power to a load (12) using the sum of outputs of the inverters (1) and (2a) to (2c). A manipulative quantity is determined so that the DC voltage at each of smoothing capacitors (3a) to (3c) which is an input of each of the single-phase sub-inverters (2a) to (2c) will follow a command value. The manipulative quantity is added to an output voltage command for the three-phase main inverter (1), and is subtracted from an output voltage command for the single-phase sub-inverters (2a) to (2c). Thus, power is shifted from the three-phase main inverter (1) to the smoothing capacitors (3a) to (3c) of the single-phase sub-inverters (2a) to (2c).