A steam turbine 10 of an embodiment has seal rings 60 between an inlet sleeve 40 for introducing steam and an inner casing 20 and an outer casing 21 into which the inlet sleeve 40 is inserted. The seal rings 60 have high-temperature side seal rings 70 which are disposed their inner circumferences contacted to the outer circumference of the inlet sleeve 40, and low-temperature side seal rings 80 which are formed to have inner and outer diameters larger than those of the high-temperature side seal rings 70 and disposed with their outer circumferences contacted to the inner casing 20 or the outer casing 21. A thermal barrier layer 90 is disposed between the inner circumferences of the high-temperature side seal rings 70 and the outer circumference of the inlet sleeve 40 and between the high-temperature side seal rings 70 and the low-temperature side seal rings 80.