Abstract: In an optical cable made by forming a sheath on enclosing one or more optical fiber cores and a tension member, high reliability is obtained through the avoidance of adverse effects on the optical fiber core of a curving tendency of the tension member prevailing over the resistance of the sheath to curving (for example, due to the installed optical cable being heated by electrical equipment in proximity) and the optical cable consequently curving. Taking the plane containing the curve formed by the tension member due to its curving tendency as a base plane, the optical fiber core is disposed in the proximity of the position of the image formed when the tension member is projected in a direction perpendicular with respect to the base plane onto a flat plane separate from and parallel with the base plane.