A gas turbine comprising: a casing wall in a cylindrical shape that forms an outer shell of a downstream side of a turbine; a bearing case that supports a bearing part of a rotor in the casing wall; a plurality of struts that are provided in a circumferential direction of the bearing case and extend in a tangential direction of the bearing case to couple the casing wall and the bearing case; a diffuser unit that includes an outer diffuser provided along an inner periphery of the casing wall and an inner diffuser provided along an outer periphery of the bearing case; a partition wall that is formed between the bearing case and the inner diffuser and covers the outer periphery of the bearing case; a cooling chamber in which the outer diffuser and the inner diffuser are coupled by a strut cover for covering each of the struts, and that leads to a portion between the casing wall and the outer diffuser, a portion between the partition wall and the inner diffuser, and an inside of the strut cover, wherein the partition wall has the struts penetrating therethrough and isolates cooling medium in the cooling chamber from cooling medium around the bearing case; and a partition wall supporting member one end side of which is fixed to the bearing case and another end side of which is fixed to the partition wall, that is provided in an extending direction of each of the struts, and that includes a sealing unit dividing the one end side and the other end side, and that is slidably provided in the extending direction of the respective strut, while maintaining airtightness between the one end side and the other end side. a casing wall in a cylindrical shape that forms an outer shell of a downstream side of a turbine; a bearing case that supports a bearing part of a rotor in the casing wall; a plurality of struts that are provided in a circumferential direction of the bearing case and extend in a tangential direction of the bearing case to couple the casing wall and the bearing case; a diffuser unit that includes an outer diffuser provided along an inner periphery of the casing wall and an inner diffuser provided along an outer periphery of the bearing case; a partition wall that is formed between the bearing case and the inner diffuser and covers the outer periphery of the bearing case; a cooling chamber in which the outer diffuser and the inner diffuser are coupled by a strut cover for covering each of the struts, and that leads to a portion between the casing wall and the outer diffuser, a portion between the partition wall and the inner diffuser, and an inside of the strut cover, wherein the partition wall has the struts penetrating therethrough and isolates cooling medium in the cooling chamber from cooling medium around the bearing case; and a partition wall supporting member one end side of which is fixed to the bearing case and another end side of which is fixed to the partition wall, that is provided in an extending direction of each of the struts, and that includes a sealing unit dividing the one end side and the other end side, and that is slidably provided in the extending direction of the respective strut, while maintaining airtightness between the one end side and the other end side.