A control device and a control method for a highly efficient power conversion device are provided. A control device for a modular multi-level power conversion device including one or more arm converters per AC phase, each having a plurality of unit converters each with an energy storage element connected in series, including: AC current control means for controls an AC current to a desired value by feedback; circulating current control means for controlling a circulating current flowing through the arm converter of each phase of the AC current of the modular multi-level power conversion device to a circulating current command value by feedback; and PWM command generation means for generating and controlling a gate signal of the unit converter configuring the arm converter according to an AC voltage target of the each AC phase obtained by correcting an output of the AC current control means according to an output of the circulating current control means, in which the circulating current control means includes circulating current command calculation means for calculating an amplitude of the circulating current command value according to a power factor of the power conversion device.