In an automatic wet sanding apparatus including a disc and a cushion pad, a disc center hole is formed at a central portion of the disc and a pad center hole is formed at a central portion of the cushion pad. Water having been supplied to an introduction space inside a skirt is stirred as an eccentric head rotates eccentrically and thereby pushed out toward a painted surface via the disc center hole and the pad center hole with enhanced pressure. Thus, sanding dust resulting from automatic wet sanding can be washed away toward an outer circumferential side by the water that is pushed out toward the outer circumferential side, so that the likelihood of clogging due to sanding dust can be reduced and high sanding efficiency can be maintained.