PURPOSE: To improve workability in installing an optical cable on a slack treatment metal fitting and improve the reliability for the optical cable after installation, as for an optical cable adapter for the slack treatment for the optical fiber when the optical fiber in strand form of the optical cable which is installed on a case body is installed on a print board unit of the case body.

CONSTITUTION: An optical cable adapter for the slack treatment for an optical cable is constituted of a division type holder fixing part 2 having a winding part 9 for the optical cable, holder movable part 3 which is constituted in pair with the division type holder fixing part 2 and can be coaxially shifted in the lateral direction and has the winding part 9, spring 4 which elastically supports holder fixing part 2 and the holder movable part 3 and always urges them in the extension direction, and a stopper 5 for regulating shift in the extension direction of the holder movable part 3.