PURPOSE: To prevent the reflected return light and multiple reflections from end faces for connection and to obviate the generation of the degradation in light transmission loss in the case of connection of optical fibers by forming slopes with a perpendicular plane only on the end faces of core parts.

CONSTITUTION: The wire-shaped core parts 1 consisting of quartz are formed with clad parts 2 on the outer peripheries thereof and are further formed with protective layers 10, 10' for coating the core parts 1 and the clad parts 2 on the outer peripheries thereof. The optical fibers 6, 6' are formed of these core parts 1 and clad parts 2. Ferrules 3, 3' of an approximately cylindrical shape provided at the ends of the connectors 4, 4' form connectors 4, 4'. The front end faces of these connectors 4, 4' are polished to the plane perpendicular to the axial line direction of the optical fibers 6, 6'. The end faces 6a, 6a' for connection of the optical fibers 6, 6' are exposed on the perpendicular faces. These end faces 6a, 6a' for connection are formed as the perpendicular faces overall and only the end faces 1a, 1a' of the core parts 1 are formed as slopes.