A partial surface treatment apparatus includes a first electrode member electrically connected to a treatment object including an outer circumferential surface and a circumferential groove, a second electrode member including an inner circumferential surface, a pair of annular-shaped elastic sealing members configured to seal a clearance between the outer circumferential surface and the inner circumferential surface, an accommodation portion accommodating each of the annular-shaped elastic sealing members, the annular-shaped elastic sealing members are movable in a diameter reduction direction, a pressure applying mechanism supplying a pressurized fluid to the annular-shaped elastic sealing members, the annular-shaped elastic sealing members are in pressure contact with the outer circumferential surface in a case where the annular-shaped elastic sealing members are moved in the diameter reduction direction, and a cutout formed at each of the annular-shaped elastic sealing members to be extended from an outer circumferential side edge portion towards the inner circumferential side.