A power conversion device is mounted with a control circuit, a plurality of drive circuits for driving switching elements in response to control signals from the control circuit, and a plurality of power supply circuits for supplying power to the drive circuits on a substrate. The power conversion device has a drive-circuit/power supply-circuit placement and wiring regions of a high current system in which the drive circuits and the power supply circuits are disposed on the substrate are provided for the respective switching elements with isolating regions interposed between the drive-circuit/power supply-circuit placement and wiring regions and the control circuit of a low current system. A gap is formed between the pairs of the drive-circuit/power supply-circuit regions. Power supply transformers are provided for transforming a voltage supplied from the control circuit for the respective power supply circuits in-between the isolating regions.