A steam turbine includes a rotary shaft configured to rotate about an axis, a rotor blade including a rotor blade body extending radially outward from the rotary shaft, and a shroud on an end outside in a radial direction, a casing enclosing the rotor blade from outside in the radial direction and including a cavity accommodating the shroud on an inner circumference of the casing, a plurality of seal fins protruding radially inward from an opposing surface that faces the shroud in the cavity such that a clearance is between an outer circumferential surface of the shroud and the plurality of seal fins, and a plurality of swirl breaks upstream of the plurality of seal fins located furthest upstream in a direction of the axis in the cavity, the plurality of swirl breaks being arranged at intervals in a circumferential direction.