A turbine comprising: a shaft body ; a plurality of turbine blades installed to surround the shaft body and disposed at a flow path through which a fluid flows; a tip shroud disposed at a tip of the turbine blades ; a diaphragm outer ring installed at a tip side of the blade via a clearance and relatively rotated with respect to the blade; and a plurality of seal fins , wherein: an annular groove having a concave cross-sectional shape is formed at an inner circumferential surface of the diaphragm outer ring , the plurality of seal fins are formed at a bottom surface of the annular groove to protrude in a radial direction, the tip shroud has a stepped cross-sectional shape, characterized in that : dead water region-filling sections are formed in spaces defined by the tip shroud , the diaphragm outer ring , and the plurality of seal fins and in which a vortex flow of the fluid is generated, such that dead water regions that the vortex flow cannot reach are filled, the dead water region-filling sections have inclined surfaces (K) along the vortex flow of the fluid, the inclined surfaces (K) are formed in concave-shaped curves in a cross-section in an axial direction thereof, the dead water region-filling sections are formed at first corners and second corners, wherein the first corners are formed by the plurality of seal fins and the bottom surface , and the second corners are formed by an axial direction wall surface and a radial direction wall surface of the tip shroud , the inclined surfaces (K) of the dead water region-filling sections of the first and second corners are oval arc-shaped, and the oval arc-shape of the first corners is elongated in the radial direction, and the oval arc-shape of the second corners is elongated in the axial direction. a shaft body ; a plurality of turbine blades installed to surround the shaft body and disposed at a flow path through which a fluid flows; a tip shroud disposed at a tip of the turbine blades ; a diaphragm outer ring installed at a tip side of the blade via a clearance and relatively rotated with respect to the blade; and a plurality of seal fins , wherein: an annular groove having a concave cross-sectional shape is formed at an inner circumferential surface of the diaphragm outer ring , the plurality of seal fins are formed at a bottom surface of the annular groove to protrude in a radial direction, the tip shroud has a stepped cross-sectional shape, an annular groove having a concave cross-sectional shape is formed at an inner circumferential surface of the diaphragm outer ring , the plurality of seal fins are formed at a bottom surface of the annular groove to protrude in a radial direction, the tip shroud has a stepped cross-sectional shape, dead water region-filling sections are formed in spaces defined by the tip shroud , the diaphragm outer ring , and the plurality of seal fins and in which a vortex flow of the fluid is generated, such that dead water regions that the vortex flow cannot reach are filled, the dead water region-filling sections have inclined surfaces (K) along the vortex flow of the fluid, the inclined surfaces (K) are formed in concave-shaped curves in a cross-section in an axial direction thereof, the dead water region-filling sections are formed at first corners and second corners, wherein the first corners are formed by the plurality of seal fins and the bottom surface , and the second corners are formed by an axial direction wall surface and a radial direction wall surface of the tip shroud , the inclined surfaces (K) of the dead water region-filling sections of the first and second corners are oval arc-shaped, and the oval arc-shape of the first corners is elongated in the radial direction, and the oval arc-shape of the second corners is elongated in the axial direction. <EOS>