a plug fixed at one end of an optical fiber cable enclosing an optical fiber;

a socket configured to be mechanically connected with the plug, said socket having a cavity of which bottom faces the end face of the optical fiber projected from the end of the optical fiber cable when mechanically connected with the plug; and

a photoelectric converter including an optical element located on the bottom of the cavity, said converter being provided for the socket;

wherein the plug is a single ferrule plug comprising:

a plug-base having a hole into which the end of the optical fiber cable is inserted, said plug-base fixing the end inserted into the hole;

a circular plug-tip having a pinhole into which the optical fiber projected from the end of the optical fiber cable is inserted; and

at least one latch formed on one part of the side face of the plug-tip;

wherein the socket further comprises:

terminals that are located on the bottom face of the socket and are electrically connected with the converter, said terminals being electrically connected with lands of a printed circuit board, respectively when the socket is mounted on the board;

a bore located at one side of the socket, said bore coming in contact with the remaining part of the side face of the plug-tip so that the plug can rotate around the pinhole when the plug is mechanically connected with the socket; and

a retainer that retains said at least one latch so as to prevent the plug-tip from falling out of the bore and to restrict a rotation angle of the plug around the pinhole within a predetermined rotation angle range, when the plug-tip is plugged in the bore.