To improve operation for opening/closing a through-hole even when a large-sized cover member is applied, and to improve appearance quality when the through-hole is covered.

The cover device for wiring is mounted inside of the through-hole 3 formed in a top plate 2, and includes: a device body 11 having a pair of mutually opposing support wall parts 111; and a cover member 12 which is movably supported by the support wall parts 111 of the device body 11 in a mode for opening/closing the through-hole 3 in the top plate 2, wherein a wiring cable is caused to pass in such a state that the cover member 12 covers the through-hole 3 in the top plate 2. An arm member 125 is oscillatably supported by the respective support wall parts 111 about the same oscillation shaft center orthogonal to the support wall parts 111, and the cover member 12 is rotatably supported about the same rotation shaft center parallel to the oscillation shaft center at the tip end of the respective arm members 125.