A turbine comprising: a sealing structure comprising a first cylinder forming a flow passage of a working fluid of a turbine therein; a second cylinder disposed at one end of the first cylinder and downstream from the flow passage; an intermediate cylinder disposed between the first and second cylinders; a first sealing part disposed at a first region between the first cylinder and the intermediate cylinder and configured to follow a positional displacement in a radial direction; and a second sealing part disposed at a second region between the second cylinder and the intermediate cylinder, and configured to follow a positional displacement in an axial direction; a stationary blade disposed in the first cylinder; and an extension part extending from the stationary blade toward a downstream side of the flow up to an end part of the first cylinder part covering an inner surface of the first cylinder part and not covering an inner surface of the intermediate cylinder part, and forming a gap with an inner surface of the first cylinder, the gap functioning as a flow passage of the cooling medium having a temperature lower than that of the working fluid, whereby the first cylinder part is in contact with the cooling medium without being in contact with the combustion gas and the second cylinder part and the intermediate cylinder part are in contact with the combustion gas without being in contact with the cooling medium. a sealing structure comprising a first cylinder forming a flow passage of a working fluid of a turbine therein; a second cylinder disposed at one end of the first cylinder and downstream from the flow passage; an intermediate cylinder disposed between the first and second cylinders; a first sealing part disposed at a first region between the first cylinder and the intermediate cylinder and configured to follow a positional displacement in a radial direction; and a second sealing part disposed at a second region between the second cylinder and the intermediate cylinder, and configured to follow a positional displacement in an axial direction; a first cylinder forming a flow passage of a working fluid of a turbine therein; a second cylinder disposed at one end of the first cylinder and downstream from the flow passage; an intermediate cylinder disposed between the first and second cylinders; a first sealing part disposed at a first region between the first cylinder and the intermediate cylinder and configured to follow a positional displacement in a radial direction; and a second sealing part disposed at a second region between the second cylinder and the intermediate cylinder, and configured to follow a positional displacement in an axial direction; a stationary blade disposed in the first cylinder; and an extension part extending from the stationary blade toward a downstream side of the flow up to an end part of the first cylinder part covering an inner surface of the first cylinder part and not covering an inner surface of the intermediate cylinder part, and forming a gap with an inner surface of the first cylinder, the gap functioning as a flow passage of the cooling medium having a temperature lower than that of the working fluid, whereby the first cylinder part is in contact with the cooling medium without being in contact with the combustion gas and the second cylinder part and the intermediate cylinder part are in contact with the combustion gas without being in contact with the cooling medium.