A gas turbine comprising: a housing; a rotor rotatable by a fluid flowing through the housing; a bearing for rotatably supporting the rotor; and a support structure configured to support the bearing with respect to the housing, the support structure comprising: an inner casing accommodating the bearing; an outer casing fastened to the housing; and a strut extending between the inner casing and the outer casing, wherein at least one of the inner casing and the outer casing comprises a diaphragm that is deformable in a radial direction of the rotor; wherein the inner casing comprises: an inner casing strut root connected to the strut; an inner casing strut platform surrounding the inner casing strut root and being formed as the diaphragm; and an inner casing main body surrounding the inner casing strut platform; and characterized in that: an inner peripheral surface of the inner casing strut root and an inner peripheral surface of the inner casing main body are spaced apart from a rotary shaft of the rotor by a first distance; an inner peripheral surface of the inner casing strut platform is spaced apart from the rotary shaft of the rotor by a second distance greater than the first distance; an outer peripheral surface of the inner casing strut platform is spaced apart from the rotary shaft of the rotor by a third distance greater than the second distance; and an outer peripheral surface of the inner casing strut root and an outer peripheral surface of the inner casing main body are spaced apart from the rotary shaft of the rotor by a fourth distance greater than the third distance, wherein the inner peripheral surface of the inner casing strut platform overlaps the outer peripheral surface of the inner casing strut platform in a radial direction of the rotor. a housing; a rotor rotatable by a fluid flowing through the housing; a bearing for rotatably supporting the rotor; and a support structure configured to support the bearing with respect to the housing, the support structure comprising: an inner casing accommodating the bearing; an outer casing fastened to the housing; and a strut extending between the inner casing and the outer casing, wherein at least one of the inner casing and the outer casing comprises a diaphragm that is deformable in a radial direction of the rotor; an inner casing accommodating the bearing; an outer casing fastened to the housing; and a strut extending between the inner casing and the outer casing, wherein at least one of the inner casing and the outer casing comprises a diaphragm that is deformable in a radial direction of the rotor; an inner casing strut root connected to the strut; an inner casing strut platform surrounding the inner casing strut root and being formed as the diaphragm; and an inner casing main body surrounding the inner casing strut platform; and characterized in that: an inner peripheral surface of the inner casing strut root and an inner peripheral surface of the inner casing main body are spaced apart from a rotary shaft of the rotor by a first distance; an inner peripheral surface of the inner casing strut platform is spaced apart from the rotary shaft of the rotor by a second distance greater than the first distance; an outer peripheral surface of the inner casing strut platform is spaced apart from the rotary shaft of the rotor by a third distance greater than the second distance; and an outer peripheral surface of the inner casing strut root and an outer peripheral surface of the inner casing main body are spaced apart from the rotary shaft of the rotor by a fourth distance greater than the third distance, wherein the inner peripheral surface of the inner casing strut platform overlaps the outer peripheral surface of the inner casing strut platform in a radial direction of the rotor. an inner peripheral surface of the inner casing strut root and an inner peripheral surface of the inner casing main body are spaced apart from a rotary shaft of the rotor by a first distance; an inner peripheral surface of the inner casing strut platform is spaced apart from the rotary shaft of the rotor by a second distance greater than the first distance; an outer peripheral surface of the inner casing strut platform is spaced apart from the rotary shaft of the rotor by a third distance greater than the second distance; and an outer peripheral surface of the inner casing strut root and an outer peripheral surface of the inner casing main body are spaced apart from the rotary shaft of the rotor by a fourth distance greater than the third distance,