To provide a cover device for a wiring box which eliminates the need for separately preparing machine screws for attachment.

A cover device 4 includes: a cover 2 having an opening 2a, through which a wiring tool passes, and attached to a wiring box 1; and machine screws 3. Machine screw holding parts 5 holding the machine screws 3 are provided in the cover 2. Each machine screw holding part 5 holds the machine screw 3 in a state where an axis of the machine screw 3 is arranged along a surface direction of a cover body 6 and faces the front side from the opening 2a. In this way, the cover 2 is attached to the wiring box 1 or the wiring tool is attached to the cover 2 by using the machine screws 3 in the cover device 4.