A turbine includes a rotor including a rotation shaft that rotates around an axis and a blade row formed on an outer surface of the rotation shaft; a casing, which covers the rotor, has a casing inner surface being expanded radially outward approaching a downstream side of the casing in a direction of the axis; and an inner member body formed to line the casing inner surface of the casing such that an extraction port is formed between an upstream side end of the inner member body and the casing inner surface. A discharge port is formed between a downstream side end of the inner peripheral member body and the casing inner peripheral surface. The extraction port and the discharge port are formed in an annular shape centered on the axis. A flow path cross-sectional area of the discharge port is smaller than that of the extraction port.