An electric power conversion apparatus includes a converter 1 for rectifying ac electric power, a series-connected set, of capacitors 2A and 2B, connected to the dc side of the converter, an inverter 3 for, by setting one end of the series-connected capacitor set to a high-potential level, the other end of the set to a low-potential level, and a connection point between the capacitors to a medium-potential level, selecting any one of the levels and outputting three-phase ac, an inverter control unit 4 for controlling the inverter 3, and a voltage measurement device 8 for measuring a capacitor voltage Vdc as a voltage between both ends of the series-connected set, of the capacitors 2A and 2B; and the inverter control unit 4 further includes a beatless control unit 21 for controlling a modulation factor γ in response to the capacitor voltage Vdc, and a frequency fixing unit 22 for fixing to a command value the frequency of an ac voltage outputted from the inverter 3.