A photoelectric converter (1C, 1E) comprising: a mount substrate; an IC circuit (50A, 50B) which is formed in an IC substrate (5A, 5B); an optical element (4A, 4B) adapted to have a function of converting an electric signal output by the IC circuit (50A, 50B) to an optical signal and emitting light, or a function of converting a received optical signal to an electric signal and outputting the electric signal to the IC circuit (50A, 50B); a waveguide (9, 31, 33, 35, 91) adapted to effect an optical coupling between the optical element (4A, 4B) and an external optical device; and an electric connector (6, 7) adapted to be provided on a surface of the mount substrate and to be capable of electrically connecting the IC circuit (50A, 50B) to an external connector, wherein: the optical element (4A, 4B) is held by the mount substrate and has a light emitting surface or a light receiving surface, the light emitting surface or the light receiving surface of the optical element (4A, 4B) being directed to the mount substrate; the waveguide (9, 31, 33, 35, 91) is provided in the mount substrate along said surface of the mount substrate; a wiring substrate adapted to change an electrode pattern is interposed between the mount substrate and the electric connector (6, 7); said photoelectric converter (1C, 1E) characterized in that: the wiring substrate includes an uppermost layer on which electrodes are formed in correspondence with the wiring pattern formed on said surface of the mount substrate, a lowermost layer on which electrodes are formed in correspondence with terminals of the electric connector (6, 7), and an intermediate layer electrically connecting the electrodes on the uppermost layer and the electrodes on the lowermost layer; the wiring substrate is connected to said surface of the mount substrate with solder balls in such a manner that a gap corresponding to the solder balls is provided between the surface and the wiring substrate; and the IC substrate (5A, 5B) and the optical element (4A, 4B) are mounted in the gap on said surface. the optical element (4A, 4B) is held by the mount substrate and has a light emitting surface or a light receiving surface, the light emitting surface or the light receiving surface of the optical element (4A, 4B) being directed to the mount substrate; the waveguide (9, 31, 33, 35, 91) is provided in the mount substrate along said surface of the mount substrate; a wiring substrate adapted to change an electrode pattern is interposed between the mount substrate and the electric connector (6, 7); the wiring substrate includes an uppermost layer on which electrodes are formed in correspondence with the wiring pattern formed on said surface of the mount substrate, a lowermost layer on which electrodes are formed in correspondence with terminals of the electric connector (6, 7), and an intermediate layer electrically connecting the electrodes on the uppermost layer and the electrodes on the lowermost layer; the wiring substrate is connected to said surface of the mount substrate with solder balls in such a manner that a gap corresponding to the solder balls is provided between the surface and the wiring substrate; and the IC substrate (5A, 5B) and the optical element (4A, 4B) are mounted in the gap on said surface.