<p>To realize an optical connector in which the optical connector plugs (411) can be inserted only in a predetermined direction or orientation into a connector housing (416) at which a plurality of optical connector plugs (411) are mounted at the highest possible mounting density, the optical connector comprising (a) an adapter housing formed with a housing cutout (425) and two opposing housing projections (424) and (b) a square cross-section optical plug (411) formed with an axially extending plug projection (419) on one side surface thereof so as to be engaged with the housing cutout (425) and with two axially extending plug grooves (418) on two opposing side surfaces thereof so as to be engaged with the two opposing housing projections (424), an outside contour of said square optical connector plug being symmetrical with respect to a plane including an axial center of said connector plug and a middle portion of the plug projection but asymmetrical with respect to the axial center of said connector plug. <IMAGE></p>
