It is an object to reduce the region of a photoelectric conversion element which light does not reach, to suppress deterioration of power generation efficiency, and to suppress manufacturing cost of a voltage conversion element. The present invention relates to a transmissive photoelectric conversion device which includes a photoelectric conversion element including an n-type semiconductor layer, an intrinsic semiconductor layer, and a p-type semiconductor layer; a voltage conversion element which is overlapped with the photoelectric conversion element and which includes an oxide semiconductor film for a channel formation region; and a conductive element which electrically connects the photoelectric conversion element and the voltage conversion element. The photoelectric conversion element is a solar cell. The voltage conversion element includes a transistor having a channel formation region including an oxide semiconductor film. The voltage conversion element is a DC-DC converter.