To provide an optical cable unit capable of being easily specified by discrimination lines stored in a cable outer sheath even when marking and characters written on the surface of the cable outer sheath are not read, and to provide an assembled optical cable comprising the optical cable units, and a method of detecting a prescribed optical cable unit.

The optical cable units 11, 11' storing and holding an optical fiber core 12 in the cable outer sheath 14 are provided with an air gap 16 in parallel to the optical fiber core 12 in the cable outer sheath 14, and loosely stores the discrimination line 17 in the air gap 16. Moreover, a display body for indicating a position of the air gap 16 may form a projected, recessed or colored band along a longitudinal direction of the cable outer sheath 14. In addition to it, the display body may provide a notch for taking out the discrimination line along the longitudinal direction of the cable outer sheath.