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 along the vortex flow of the fluid, the inclined surfaces 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 (521a,521b) and a radial direction wall surface (522b,522c) of the tip shroud, the inclined surfaces 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 along the vortex flow of the fluid, the inclined surfaces 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 (521a,521b) and a radial direction wall surface (522b,522c) of the tip shroud, the inclined surfaces 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.