To make it possible to fix the ends of a plurality of optical fibers in a parallel state into through-holes of a circular shape in the cross-sectional shape formed in a ferrule.

The ends 10a, 10b of the optical fiber are inserted into the through-hole of the circular shape in the cross-sectional shape formed in the ferrule 14 in this structure. The one through-hole 16a and another through-hole 16b which are bored in the ferrule 14 and vary in bores are formed in parallel and tight contact with each other. A slit for connecting the through-holes to each other is formed along the through-holes 16a, 16b at the boundary where the one through-hole 16a and the other through-hole 16b come into contact with each other. In addition, the ends 10a, 10b of the optical fibers respectively inserted into the through-holes 16a, 16b are fixed by solidifying of a liquid adhesive 18 inserted into the through-holes 16a, 16b in such a manner that the outer peripheral surface at the end 10b of the optical fiber inserted into the other through-hole 16b is brought into contact with the outer peripheral surface of the end 10a of the optical fiber inserted into the one through-hole 16a formed to the diameter smaller than the diameter of the inside wall surface of the other through- hole 16b in sliding contact therewith and is fixed thereto at the point of the slit described above.