A power conversion device achieves size reduction and reliability by reducing the number of components of the system. The power conversion device has a semiconductor module of a half-bridge configuration in which two semiconductor elements are arranged in series. The semiconductor module has a cuboidal shape and has, along a longitudinal direction thereof, a positive pole terminal, a negative pole terminal, and terminals for inputting or outputting alternating current or for forming a single phase of the power conversion device. In the vertical direction corresponding to a widthwise direction of the cuboid, a plurality of the semiconductor modules are arranged vertically, forming a plurality of phases of the power conversion device. The semiconductor modules of the plurality of phases are installed in contact with a cooling unit, and one or more capacitors are disposed so as to face the cooling unit across the semiconductor modules of the plurality of phases.