A multi-chip module having an optical element sending and receiving optical signals and mounted on a printed circuit board in which an optical guide is formed, includes an optical path-converting member that protrudes from a face of the multi-chip module that is to be connected to the printed circuit board, is optically connected to the optical element, and is inserted into an inserting hole formed on the printed circuit board so as to intersect the optical guide when mounting the multi-chip module. The optical path-converting member is inserted into the inserting hole to form an optical path guiding light from the optical element into the optical guide or guiding light transmitted through the optical guide into the optical element.