Combined generator system

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The present invention relates to a steam turbine comprising a rotor shaft (3) integrating high and low pressure portions provided with blades (4) at the final stage thereof having a length not less than 30 inches, wherein a steam temperature at first stage blades (4) is 530 DEG C, a ratio (L/D) of a length (L) defined between bearings (12) of the rotor shaft (3) to a diameter (D) measured between the terminal ends of final stage blades (4) is 1.4 to 2.3. This rotor shaft (3) is composed of heat resisting steel containing by weight 0.15 to 0.4% C, not more than 0.1% Si, 0.05 to 0.25% Mn, 1.5 to 2.5% Ni, 0.8 to 2.5% Cr, 0.8 to 2.5% Mo and 0.15 to 0.35% V and, further, the heat resisting steel may contain at least one of Nb, Ta, W, Ti, Al, Zr, B, Ca, and rare earth elements.