A power conversion device in which the inductance of a main circuit is reduced, a surge voltage is suppressed, elements are properly cooled, which is miniaturized and reduced in weight as a whole, and is excellent in handling performance in a manufacturing process and a maintenance work. A positive side arm unit includes IGBT modules, a coupling diode module, a cooling plate on which the modules are mounted, and a first laminated bus bar connected to the respective modules. A negative side arm unit includes IGBT modules, a coupling diode module, a cooling plate on which the modules are mounted, and a second laminated bus bar connected to the respective modules, and both the laminated bus bars and the capacitors are connected to one another by a third laminated bus bar. Both the cooling plates are parallel to each other so that the mount surfaces thereof are set in the same direction.