A power conversion device comprising: - a power converter including a plurality of phase arms (4U, 4V, 4W) in which a first arm (5U, 5V, 5W) and a second arm (6U, 6V, 6W) for each of phases are connected in series to each other, the plurality of phase arms (4U, 4V, 4W) being connected in parallel between positive and negative DC lines, the power converter configured for performing power conversion between three-phase AC and DC; and - a control device (50, 50A, 50B) which is configured to generate respective voltage command values for the first arm (5U, 5V, 5W) and the second arm (6U, 6V, 6W) and to perform drive-control of the power converter on the basis of the voltage command values, wherein the first arm (5U, 5V, 5W) and the second arm (6U, 6V, 6W) each include a converter cell (10, 20, 20a) composed of: a first series body (23,35) having semiconductor switching elements (21s, 22s, 31s, 32s) in both of upper and lower arms; and a DC capacitor (29, 39) connected in parallel to the first series body (23,35), the converter cell (20, 20a) in the second arm (6U, 6V, 6W) is a second converter cell (20, 20a) formed by connecting the DC capacitor, the first series body (23,35), and a second series body (36,36a) in parallel, the second series body (36,36a) having a semiconductor switching element in one of upper and lower arms and a diode (33, 37d) in the other one, the second converter cell (20, 20a) being configured to output positive-polarity and negative-polarity voltages corresponding to a magnitude of both-end voltage of the DC capacitor, when short-circuit between the DC lines is detected, the control device (50, 50A, 50B) is configured to perform protection control to turn off the semiconductor switching elements (21s, 22s, 31s, 32s, 34s, 37s) in the power converter, and characterized in that, when elimination of the short-circuit between the DC lines is detected, the control device (50, 50A, 50B) is configured to perform restart of control of the power converter and give a voltage command value including a positive-polarity DC voltage command value, to the converter cell in the first arm (5U, 5V, 5W), and to give a voltage command value including a DC voltage command value that gradually increases from a negative polarity to a positive polarity, to the second converter cell (20, 20a) in the second arm (6U, 6V, 6W), thereby outputting DC voltage that gradually increases, to the DC lines, while causing a negative-polarity current flowing through the diode (33, 37d) to flow to the phase arm (4U, 4V, 4W), using an impedance (ZP, ZN) that the DC lines have. - a power converter including a plurality of phase arms (4U, 4V, 4W) in which a first arm (5U, 5V, 5W) and a second arm (6U, 6V, 6W) for each of phases are connected in series to each other, the plurality of phase arms (4U, 4V, 4W) being connected in parallel between positive and negative DC lines, the power converter configured for performing power conversion between three-phase AC and DC; and - a control device (50, 50A, 50B) which is configured to generate respective voltage command values for the first arm (5U, 5V, 5W) and the second arm (6U, 6V, 6W) and to perform drive-control of the power converter on the basis of the voltage command values, wherein the first arm (5U, 5V, 5W) and the second arm (6U, 6V, 6W) each include a converter cell (10, 20, 20a) composed of: a first series body (23,35) having semiconductor switching elements (21s, 22s, 31s, 32s) in both of upper and lower arms; and a DC capacitor (29, 39) connected in parallel to the first series body (23,35), the converter cell (20, 20a) in the second arm (6U, 6V, 6W) is a second converter cell (20, 20a) formed by connecting the DC capacitor, the first series body (23,35), and a second series body (36,36a) in parallel, the second series body (36,36a) having a semiconductor switching element in one of upper and lower arms and a diode (33, 37d) in the other one, the second converter cell (20, 20a) being configured to output positive-polarity and negative-polarity voltages corresponding to a magnitude of both-end voltage of the DC capacitor, when short-circuit between the DC lines is detected, the control device (50, 50A, 50B) is configured to perform protection control to turn off the semiconductor switching elements (21s, 22s, 31s, 32s, 34s, 37s) in the power converter, and characterized in that, when elimination of the short-circuit between the DC lines is detected, the control device (50, 50A, 50B) is configured to perform restart of control of the power converter and give a voltage command value including a positive-polarity DC voltage command value, to the converter cell in the first arm (5U, 5V, 5W), and to give a voltage command value including a DC voltage command value that gradually increases from a negative polarity to a positive polarity, to the second converter cell (20, 20a) in the second arm (6U, 6V, 6W), thereby outputting DC voltage that gradually increases, to the DC lines, while causing a negative-polarity current flowing through the diode (33, 37d) to flow to the phase arm (4U, 4V, 4W), using an impedance (ZP, ZN) that the DC lines have.