In a power conversion module device of the present invention, transformer (11), primary power element (14), and secondary power element (15) are mounted on printed wiring board (16) in surface-to-surface contact therewith, and no control circuit is mounted thereon. In addition to reduction in impedance and loss in the wiring, this constitution improves the voltage waveform of primary power element (14). Thus, noise reduction can be achieved. Further, because heat can be transferred to printed wiring board (16), heat generated from transformer (11), primary power element (14), and secondary power element (15) can be reduced. The size of the transformer can also be reduced.