A variable nozzle unit disposed between a turbine scroll passage and a gas discharge port inside a turbine housing of a variable-geometry turbocharger in such a way as to surround a turbine impeller, and capable of changing a passage area for an exhaust gas to be supplied to the turbine impeller side, comprising: a nozzle ring disposed inside the turbine housing; a shroud ring provided integrally with the nozzle ring at a position away from and opposed to the nozzle ring and including a cylindrical shroud portion placed on an inner peripheral edge side, projecting to the gas discharge port side, and being configured to occlude outer edges of a plurality of turbine blades of the turbine impeller, the shroud portion being placed on an inside of an annular step portion formed on an inlet side of the gas discharge port inside the turbine housing, and the shroud ring including a ring groove formed in an outer peripheral surface of the shroud portion; a plurality of variable nozzles disposed in a circumferential direction between opposed surfaces of the nozzle ring and the shroud ring, each variable nozzle being turnable in forward and reverse directions about a shaft center in parallel with a shaft center of the turbine impeller; and first and second seal rings (83, 85) provided with inner peripheral edge portions being fitted into the ring groove of the shroud ring and being configured to suppress leakage of the exhaust gas from the turbine scroll passage side, wherein: the first and second seal rings (83, 85) are provided in pressure-contact by their own elastic forces with an inner peripheral surface of the step portion of the turbine housing; and the second ring is located closer to the gas discharge port than the first ring; characterized in that: a seal flange projecting in a downstream direction is formed at an inner peripheral edge portion of the first seal ring, when the first and second seal rings are viewed from radially inside, the seal flange of the first seal ring is designed to at least partially occlude an end gap of the second seal ring; and the first and second rings are made of materials having same linear expansion coefficient. a nozzle ring disposed inside the turbine housing; a shroud ring provided integrally with the nozzle ring at a position away from and opposed to the nozzle ring and including a cylindrical shroud portion placed on an inner peripheral edge side, projecting to the gas discharge port side, and being configured to occlude outer edges of a plurality of turbine blades of the turbine impeller, the shroud portion being placed on an inside of an annular step portion formed on an inlet side of the gas discharge port inside the turbine housing, and the shroud ring including a ring groove formed in an outer peripheral surface of the shroud portion; the shroud portion being placed on an inside of an annular step portion formed on an inlet side of the gas discharge port inside the turbine housing, and the shroud ring including a ring groove formed in an outer peripheral surface of the shroud portion; a plurality of variable nozzles disposed in a circumferential direction between opposed surfaces of the nozzle ring and the shroud ring, each variable nozzle being turnable in forward and reverse directions about a shaft center in parallel with a shaft center of the turbine impeller; and first and second seal rings (83, 85) provided with inner peripheral edge portions being fitted into the ring groove of the shroud ring and being configured to suppress leakage of the exhaust gas from the turbine scroll passage side, wherein: the first and second seal rings (83, 85) are provided in pressure-contact by their own elastic forces with an inner peripheral surface of the step portion of the turbine housing; and the second ring is located closer to the gas discharge port than the first ring; the first and second seal rings (83, 85) are provided in pressure-contact by their own elastic forces with an inner peripheral surface of the step portion of the turbine housing; and the second ring is located closer to the gas discharge port than the first ring; characterized in that: a seal flange projecting in a downstream direction is formed at an inner peripheral edge portion of the first seal ring, when the first and second seal rings are viewed from radially inside, the seal flange of the first seal ring is designed to at least partially occlude an end gap of the second seal ring; and the first and second rings are made of materials having same linear expansion coefficient. a seal flange projecting in a downstream direction is formed at an inner peripheral edge portion of the first seal ring, when the first and second seal rings are viewed from radially inside, the seal flange of the first seal ring is designed to at least partially occlude an end gap of the second seal ring; and the first and second rings are made of materials having same linear expansion coefficient.