Turbine

A turbine comprising:

• a rotor including:
• a rotation shaft that rotates around an axis of the rotation shaft;
• and
• blade rows on an outer peripheral surface of the rotation shaft that are separated from each other in a direction of the axis;
• a casing covering an outer circumference of the rotor and that has a casing inner peripheral surface expanding radially outward toward downstream of the casing;
• and
• an inner peripheral member body that:
• extends over the casing inner peripheral surface of the casing, and forms:
• an extraction port between an upstream side end of the inner peripheral member body and the casing inner peripheral surface, and
• a discharge port between a downstream side end of the inner peripheral member body and the casing inner peripheral surface,
• wherein the inner peripheral member body is separated in a radial direction of the rotor from a final stage blade row that is disposed on a most downstream side of the blade rows and faces at least a portion of the final stage blade row in the radial direction,
• wherein the extraction port is disposed upstream of a downstream end of the final stage blade row,
• wherein the discharge port is disposed downstream of the final stage blade row,
• wherein the extraction port and the discharge port are in an annular shape centered on the axis, and
• wherein a flow path cross-sectional area of the discharge port is smaller than a flow path cross-sectional area of the extraction port.