A command device is connected with a serial line to a driving device for controlling operations of a plurality of first switching elements and one or more second switching elements. The command device includes a command signal generator to generate a plurality of first command signals and one or more second command signals, an encoder to generate encoded data by encoding at least some signals of the plurality of first command signals and the one or more second command signals, and a command-device serializer to generate serial command data through serial conversion of the encoded data and transmit the serial command data to the driving device via the serial line.