Turbine rotor and steam turbine

A steam turbine to which high-temperature steam is introduced and which comprises a turbine rotor penetratingly provided in the steam turbine, wherein said turbine rotor comprises:

• a high-temperature turbine rotor constituent part where the high-temperature steam passes;
• low-temperature turbine rotor constituent parts sandwiching and weld-connected to said high-temperature turbine rotor constituent part and made of a material different from a material of said high-temperature turbine rotor constituent part;
• and
• a cooling part cooling said high-temperature turbine rotor constituent part by ejecting cooling steam to a position, of said high-temperature turbine rotor constituent part, near a welded portion between said high-temperature turbine rotor constituent part and said low-temperature turbine rotor constituent part, and
• wherein a value equal to a distance divided by a diameter is equal to or more than 0.3, where the distance is a distance from the position, of said high-temperature turbine rotor constituent part, ejected the cooling steam by said cooling part up to the welded portion, and the diameter is a turbine rotor diameter of said high-temperature turbine rotor constituent part.