A regenerative gas turbine combustor, comprising: a combustor inner cylinder internally defining a combustion chamber; a tail cylinder connecting the combustor inner cylinder with a turbine; a combustor outer cylinder surrounding the combustor inner cylinder and the tail cylinder; a fuel nozzle for supplying fuel to the combustion chamber; a bleeding port provided in the combustor outer cylinder; a regenerator for preheating, by using the exhaust gas from the turbine, compressed air bled from the bleeding port; an injection port for injecting the compressed air preheated by the regenerator into the inside of the combustor outer cylinder; a division wall for blocking a compressed-air passage located between the combustor inner cylinder and the tail cylinder, and the combustor outer cylinder, at a position between the bleeding port and the injection port; and a sealing mechanism for sealing a clearance between the tail cylinder or the combustor inner cylinder and the division wall; characterized in that the sealing mechanism includes a plurality of seal rings (17a-17c) provided in an axial direction of the tail cylinder; a holder installed on an inner circumferential portion of the division wall and having a ring groove (25a-25c) for holding the seal rings (17a-17c) and a gap provided between an inner circumferential surface of the ring groove (25a-25c) and an outer circumferential surface of the seal ring (17a-17c); wherein the holder includes a holder body, a spacer (18a, 18b) interposed between the seal rings (17a-17c) adjacent to each other and defining the ring groove(25a-25c), and a pressing force adjusting mechanism for adjusting the pressing force of the seal rings (17a-17c) and the spacer (18a, 18b) against the holder body. a combustor inner cylinder internally defining a combustion chamber; a tail cylinder connecting the combustor inner cylinder with a turbine; a combustor outer cylinder surrounding the combustor inner cylinder and the tail cylinder; a fuel nozzle for supplying fuel to the combustion chamber; a bleeding port provided in the combustor outer cylinder; a regenerator for preheating, by using the exhaust gas from the turbine, compressed air bled from the bleeding port; an injection port for injecting the compressed air preheated by the regenerator into the inside of the combustor outer cylinder; a division wall for blocking a compressed-air passage located between the combustor inner cylinder and the tail cylinder, and the combustor outer cylinder, at a position between the bleeding port and the injection port; and a sealing mechanism for sealing a clearance between the tail cylinder or the combustor inner cylinder and the division wall; characterized in that the sealing mechanism includes a plurality of seal rings (17a-17c) provided in an axial direction of the tail cylinder; a holder installed on an inner circumferential portion of the division wall and having a ring groove (25a-25c) for holding the seal rings (17a-17c) and a gap provided between an inner circumferential surface of the ring groove (25a-25c) and an outer circumferential surface of the seal ring (17a-17c); wherein the holder includes a holder body, a spacer (18a, 18b) interposed between the seal rings (17a-17c) adjacent to each other and defining the ring groove(25a-25c), and a pressing force adjusting mechanism for adjusting the pressing force of the seal rings (17a-17c) and the spacer (18a, 18b) against the holder body.