PURPOSE: To enable coupling of extremely small axial-shaft by a method wherein an optical fiber is sealed by fixing to a light emitting and a light receiving element with active rays and hardened type resin composite.

CONSTITUTION: The optical fiber is sealed by fixing to the light emitting element and/or the light receiving element with active rays and hardened type resin composite hardening on heating. The used resin composite is hardened with active rays and on heating. Particularly, a hardened type resin composite, containing a compound (A) having at least two epoxy groups in a molecule, a photopolymerized compound (B) having a carboxyl group in a molecule, or the mixture of said compound (B) and another photopolymerized compound (C), is used.