A gas turbine (1;2;3) comprising: a compressor unit, a combustor unit, a turbine unit, and an exhaust unit in order from an upstream side to a downstream side of flow of fluid through the gas turbine in operation; a casing (60;260;360) including a compressor casing, a combustor casing, a turbine unit casing, and an exhaust casing; a rotor provided inside the casing (60;260;360) so as to penetrate the central parts of the compressor unit, the combustor unit, the turbine unit, and the exhaust unit and so as to be rotatable around a rotation axis; wherein the casing (60;260;360) is divided at divided portions on a plane including the rotation axis of the rotor and at divided portions on plural planes perpendicular to the rotation axis of the rotor along the axial direction of the rotor such that a plurality of lower casing parts (61D,62D,63D,64D,65D,66D) and a plurality of upper casing parts (61U,62U,63U,64U,65U,66U) are formed; wherein adjacent ones of the plurality of lower casing parts (61D, 62D, 63D, 64D, 65D, 66D) and upper casing parts (61U,62U,63U,64U,65U,66U) are respectively connected to each other at flanges formed at the divided portions, wherein lateral flanges are formed at the divided portion on the plane including the rotation axis and are formed parallel to the rotation axis of the rotor, and longitudinal flanges are formed at the divided portions on the planes orthogonal to the rotation axis and are formed along a circumferential direction on a side periphery of the casing, wherein the longitudinal flanges of the upper casing part forming the combustor casing and covering the combustor and the combustor chamber of the combustor unit are formed at divided portions at planes at an axial position along the rotor located in the compressor unit and in the turbine unit, respectively. a compressor unit, a combustor unit, a turbine unit, and an exhaust unit in order from an upstream side to a downstream side of flow of fluid through the gas turbine in operation; a casing (60;260;360) including a compressor casing, a combustor casing, a turbine unit casing, and an exhaust casing; a rotor provided inside the casing (60;260;360) so as to penetrate the central parts of the compressor unit, the combustor unit, the turbine unit, and the exhaust unit and so as to be rotatable around a rotation axis; wherein the casing (60;260;360) is divided at divided portions on a plane including the rotation axis of the rotor and at divided portions on plural planes perpendicular to the rotation axis of the rotor along the axial direction of the rotor such that a plurality of lower casing parts (61D,62D,63D,64D,65D,66D) and a plurality of upper casing parts (61U,62U,63U,64U,65U,66U) are formed; wherein adjacent ones of the plurality of lower casing parts (61D, 62D, 63D, 64D, 65D, 66D) and upper casing parts (61U,62U,63U,64U,65U,66U) are respectively connected to each other at flanges formed at the divided portions, wherein lateral flanges are formed at the divided portion on the plane including the rotation axis and are formed parallel to the rotation axis of the rotor, and longitudinal flanges are formed at the divided portions on the planes orthogonal to the rotation axis and are formed along a circumferential direction on a side periphery of the casing, wherein the longitudinal flanges of the upper casing part forming the combustor casing and covering the combustor and the combustor chamber of the combustor unit are formed at divided portions at planes at an axial position along the rotor located in the compressor unit and in the turbine unit, respectively.