A steam turbine comprising: a turbine rotor including a shaft member and a plurality of seals connected to the shaft member, the shaft member extending in an axial direction (X axis); a turbine casing disposed around the turbine rotor with a turbine casing space formed between the turbine casing and the turbine rotor; and a gland casing connected to an axial end of the turbine casing and including an outer gland axially disposed so as to close an opening at an axial end of the turbine casing space from the outside, and an inner gland axially disposed so as to provide a gland space between the inner gland and the outer gland, wherein the outer gland and the inner gland each include a first annular section having a first joint surface and a second annular section having a second joint surface joined to the first joint surface, the first annular section being disposed around a part of the turbine rotor, the second annular section being disposed around another part of the turbine rotor, and wherein a gland steam is supplied into the gland space and said plurality of seals is provided between the shaft member and the inner gland and between the shaft member and the outer gland, and wherein the inner gland includes an annular protrusion extending in an axial direction from the inner gland toward the outer gland; the steam turbine further comprising: a heat insulation space defined by a radially inner surface of the turbine casing, a radially inner surface of the outer gland, the inner gland including a radially outer facing surface of the protrusion, and a sealing mechanism, wherein the sealing mechanism is disposed between the radially inner surface of the outer gland and the radially outer facing surface of the protrusion to prevent the gland steam in the gland space from flowing into the heat insulation space. a turbine rotor including a shaft member and a plurality of seals connected to the shaft member, the shaft member extending in an axial direction (X axis); a turbine casing disposed around the turbine rotor with a turbine casing space formed between the turbine casing and the turbine rotor; and a gland casing connected to an axial end of the turbine casing and including an outer gland axially disposed so as to close an opening at an axial end of the turbine casing space from the outside, and an inner gland axially disposed so as to provide a gland space between the inner gland and the outer gland, wherein the outer gland and the inner gland each include a first annular section having a first joint surface and a second annular section having a second joint surface joined to the first joint surface, the first annular section being disposed around a part of the turbine rotor, the second annular section being disposed around another part of the turbine rotor, and wherein a gland steam is supplied into the gland space and said plurality of seals is provided between the shaft member and the inner gland and between the shaft member and the outer gland, and wherein the inner gland includes an annular protrusion extending in an axial direction from the inner gland toward the outer gland; a heat insulation space defined by a radially inner surface of the turbine casing, a radially inner surface of the outer gland, the inner gland including a radially outer facing surface of the protrusion, and a sealing mechanism, wherein the sealing mechanism is disposed between the radially inner surface of the outer gland and the radially outer facing surface of the protrusion to prevent the gland steam in the gland space from flowing into the heat insulation space.