PURPOSE: To improve resistance performance to external force and to eliminate the need for unitization by providing the 2nd sheath layer via a lubricating layer on the 1st sheath layer provided on optical transmission strands and providing further the 3rd sheath layer via a reinforcing fiber layer thereon.

CONSTITUTION: The 2nd sheath layer 8 is provided via a lubricating layer 7 on the 1st sheath layer 6 provided on optical transmission strands 4, 5 and further the 3rd sheath layer 10 is provided via a reinforcing fiber layer 9 thereon. The layer 7 is formed of a viscous material having ≥500cp viscosity. The layer 8, the layer 9 and the layer 10 are united to one body by thermal fusion and the layer 8 and the layer 10 are formed of a plastic having 100W1,000kg/mm2 modulus of elasticity in tension. The space between the layer 6 and the layer 8 is adequately maintained by the layer 7 of such constitution and the outflow of a lubricating agent does not arise. The resistance performance to external force from the lateral direction is obtd. and adequate resilience is obtd. by the unification of the layer 8, the layer 9 and the layer 10. The need for unitization is thus eliminated, and the fiber is made compact, is easily connectable and highly reliable against external force. The transmission loss of light is decreased and the fiber is usable for a submarine suspended composite cable, etc. on which the external force acts for a long time.