A power conversion device comprising: a DC power source; a plurality of main circuit switching elements constituting a positive arm and a negative arm which are bridge-connected so as to convert DC of the DC power source into AC; a plurality of high-speed diodes connected in reverse parallel to the main circuit switching elements, respectively; and a plurality of gate driving circuits (8, 8u, 8v, 8w, 8x, 8y, 8z) that perform switching of the main circuit switching elements, respectively, at a desired timing, the main circuit switching elements constituting the positive arm including a normally-on switching element, a normally-off switching element whose positive terminal is connected to the negative terminal of the normally-on switching element, and a cascode-connecting diode series-connected between the gate of the normally-on switching element and the normally-off switching element in a forward direction, characterized in that: the main circuit switching elements constituting the negative arm including normally-on switching elements provided for respective phases, a normally-off switching element shared by respective phases and whose positive terminal is connected to the negative terminals of the normally-on switching elements, and a plurality of cascode-connecting diodes series-connected between each of the gates of the normally-on switching element and the negative terminal of the normally-off switching element, and each of the gate driving circuits (8u, 8v, 8w) for the positive arm is connected to the gate of a corresponding normally-on switching element and a corresponding normally-off switching element constituting the main circuit switching elements, each of the gate driving circuits (8x, 8y, 8z) for the negative arm is connected to the gate of a corresponding normally-on switching element constituting the main circuit switching elements, and one gate driving circuit for the negative arm is connected to the gate of the shared normally-off switching element. a DC power source; a plurality of main circuit switching elements constituting a positive arm and a negative arm which are bridge-connected so as to convert DC of the DC power source into AC; a plurality of high-speed diodes connected in reverse parallel to the main circuit switching elements, respectively; and a plurality of gate driving circuits (8, 8u, 8v, 8w, 8x, 8y, 8z) that perform switching of the main circuit switching elements, respectively, at a desired timing, the main circuit switching elements constituting the positive arm including a normally-on switching element, a normally-off switching element whose positive terminal is connected to the negative terminal of the normally-on switching element, and a cascode-connecting diode series-connected between the gate of the normally-on switching element and the normally-off switching element in a forward direction, characterized in that: the main circuit switching elements constituting the negative arm including normally-on switching elements provided for respective phases, a normally-off switching element shared by respective phases and whose positive terminal is connected to the negative terminals of the normally-on switching elements, and a plurality of cascode-connecting diodes series-connected between each of the gates of the normally-on switching element and the negative terminal of the normally-off switching element, and each of the gate driving circuits (8u, 8v, 8w) for the positive arm is connected to the gate of a corresponding normally-on switching element and a corresponding normally-off switching element constituting the main circuit switching elements, each of the gate driving circuits (8x, 8y, 8z) for the negative arm is connected to the gate of a corresponding normally-on switching element constituting the main circuit switching elements, and one gate driving circuit for the negative arm is connected to the gate of the shared normally-off switching element. the main circuit switching elements constituting the negative arm including normally-on switching elements provided for respective phases, a normally-off switching element shared by respective phases and whose positive terminal is connected to the negative terminals of the normally-on switching elements, and a plurality of cascode-connecting diodes series-connected between each of the gates of the normally-on switching element and the negative terminal of the normally-off switching element, and each of the gate driving circuits (8u, 8v, 8w) for the positive arm is connected to the gate of a corresponding normally-on switching element and a corresponding normally-off switching element constituting the main circuit switching elements, each of the gate driving circuits (8x, 8y, 8z) for the negative arm is connected to the gate of a corresponding normally-on switching element constituting the main circuit switching elements, and one gate driving circuit for the negative arm is connected to the gate of the shared normally-off switching element.