PURPOSE: To hold transmission and mechanical characteristics in a satisfactory state, by forming an optical fiber core as one body mechanically with a cable constituting member by a part of a core holding spacer which is extruded cylindrically on a tension member, and absorbing the elongation due to mechanical tension, and the expansion and contraction due to a temperature change.

CONSTITUTION: 2 optical fiber cores 1 are wound laterally. On a tension member 6 consisting of a metallic wire or a reinforced plastic wire, core holding spacers 7aW7c consisting of rubber or plastic are provided at each prescribed interval. A clamping collar 8 executes operation for fixing the spirally wound core 1 to the core holding spacer by guiding the outside circumference of the core holding spacer. The space in which the core exists, between the core holding spacers is filled with a waterproof compound 9. The core 1 secures necessary and sufficient surplus length in this part. Also, by a plastic tube 10 and a cable sheath 11 consisting of a metallic pipe, the whole body is sheathed so as to cover the outside circumference of the spacers 7aW7c.