A polishing apparatus comprising: a polishing head for holding a work; a polishing plate having a polishing face, on which a polishing pad is adhered; and a driving mechanism for relatively moving the polishing head with respect to the polishing plate, and wherein the polishing head includes: a holding plate having a ring-shaped side wall (22a, 22b); an elastic sheet member being fixed to an edge of the holding plate, the elastic sheet member having a lower face, which is capable of pressing the work onto the polishing pad of the polishing plate; a pressure chamber, to which a fluid at a prescribed pressure is supplied so as to press the elastic sheet member, being formed between a lower face of the holding plate and an upper face of the elastic sheet member; a seal ring concentrically dividing the pressure chamber into chambers (40, 42), the seal ring having a contact portion, which contacts the elastic sheet member so as to divide the pressure chamber into inner and outer divided chambers, and a main body part by which it is mounted; and a fluid supply section (29, etc.) for individually supplying the fluid to the divided chambers (40, 42), which are divided by the seal ring; characterised in that: a circular supporting plate is fixed in a space surrounded by the ring-shaped side wall (22a,22b) of the holding plate; the seal ring is a rubber V-ring having said main body part and a seal lip, wherein the main body part is mounted on an outer circumferential face of the supporting plate; and the seal lip is said contact portion and slopingly contacts the elastic sheet member so that, in use, the seal lip can slightly open to allow passage of fluid from a first one of said chambers (40,42) which is at a higher pressure to the other one of said chambers (42,40) which is at a lower pressure, but passage of fluid in the opposite direction is not permitted since relatively higher pressure in said other one of said chambers (42,40) tends to close seal lip. a polishing head for holding a work; a polishing plate having a polishing face, on which a polishing pad is adhered; and a driving mechanism for relatively moving the polishing head with respect to the polishing plate, and wherein the polishing head includes: a holding plate having a ring-shaped side wall (22a, 22b); an elastic sheet member being fixed to an edge of the holding plate, the elastic sheet member having a lower face, which is capable of pressing the work onto the polishing pad of the polishing plate; a pressure chamber, to which a fluid at a prescribed pressure is supplied so as to press the elastic sheet member, being formed between a lower face of the holding plate and an upper face of the elastic sheet member; a seal ring concentrically dividing the pressure chamber into chambers (40, 42), the seal ring having a contact portion, which contacts the elastic sheet member so as to divide the pressure chamber into inner and outer divided chambers, and a main body part by which it is mounted; and a fluid supply section (29, etc.) for individually supplying the fluid to the divided chambers (40, 42), which are divided by the seal ring; a holding plate having a ring-shaped side wall (22a, 22b); an elastic sheet member being fixed to an edge of the holding plate, the elastic sheet member having a lower face, which is capable of pressing the work onto the polishing pad of the polishing plate; a pressure chamber, to which a fluid at a prescribed pressure is supplied so as to press the elastic sheet member, being formed between a lower face of the holding plate and an upper face of the elastic sheet member; a seal ring concentrically dividing the pressure chamber into chambers (40, 42), the seal ring having a contact portion, which contacts the elastic sheet member so as to divide the pressure chamber into inner and outer divided chambers, and a main body part by which it is mounted; and a fluid supply section (29, etc.) for individually supplying the fluid to the divided chambers (40, 42), which are divided by the seal ring; a circular supporting plate is fixed in a space surrounded by the ring-shaped side wall (22a,22b) of the holding plate; the seal ring is a rubber V-ring having said main body part and a seal lip, wherein the main body part is mounted on an outer circumferential face of the supporting plate; and the seal lip is said contact portion and slopingly contacts the elastic sheet member so that, in use, the seal lip can slightly open to allow passage of fluid from a first one of said chambers (40,42) which is at a higher pressure to the other one of said chambers (42,40) which is at a lower pressure, but passage of fluid in the opposite direction is not permitted since relatively higher pressure in said other one of said chambers (42,40) tends to close seal lip.