To provide a cable rack cover mounting structure that has high workability and safety by allowing the mounting and removing work of a bottom surface side cover to be performed independently from cable rack arranging (coupling) work, and that has high quake-proof by being mounted strongly.

A cable rack is formed by providing sub girders 2 at a prescribed interval between a pair of main girders 1 facing each other. A portion between ends of a pair of the main girders 1 of the cable rack is regarded as a cable inserting side opening, and a portion between other ends as the bottom surface side opening. A bottom surface side cover 3 is arranged between end edges facing each other of the bottom surface side opening of a pair of the main girders 1. The bottom surface side cover 3 is mounted with members attached to the cable rack for mounting the bottom surface side cover 3.