PURPOSE: To reduce a coupling loss of a light emitting element and a photodetector, and an optical fiber by providing a condensing lens and a parallel beam forming lens on a light emitting end and a photodetecting end.

CONSTITUTION: A light passing through an optical fiber 2 of an optical connector 1 is formed to a parallel beam, made incident to a photodetector 4 in a receptacle 3, and converted to an electrical signal. With regard to a light emitting end part, too, in the same way, a light from a light emitting element 7 becomes radial temporarily, but it is condensed by a condensing lens 10 consisting of a cylindrical plane end lens, coupled with the optical fiber 2 of the optical connector 1 and transmitted. The convex lens is a cylindrical plane end lens, and it is constituted so that the refractive index becomes smaller toward the outside from the center of a circle. The focal distance is determined by a length of the cylinder, and a focus exists in the end of the cylider.