Steam turbine

A steam turbine, comprising:

• a turbine rotor penetratingly provided in a casing, and having a plurality of stages of rotor disks projected to an outside in a radial direction along a circumferential direction, in a turbine rotor axial direction;
• rotor blade cascades each configured by implanting a plurality of rotor blades in the rotor disk in the circumferential direction;
• stationary blade cascades each configured by supporting a plurality of stationary blades in the circumferential direction between a diaphragm outer ring and a diaphragm inner ring provided on an inside of the casing, and each arranged alternately with the rotor blade cascade in the turbine rotor axial direction;
• and
• a steam passage formed on a turbine stage, among a plurality of turbine stages each configured by the stationary blade cascade and the rotor blade cascade arranged at an immediately downstream side of the stationary blade cascade, including the rotor blades each having a blade height equal to or more than a blade height at which a loss generated when a leakage steam flown downstream between the diaphragm inner ring and the turbine rotor jets into a main steam from a portion between the diaphragm inner ring and the rotor blades and a benefit brought by increasing the blade height of each of the rotor blades in accordance with an increase in a flow rate of the main steam due to the jet of the leakage steam into the main steam are cancelled, and leading the leakage steam from an upstream side to a downstream side of the rotor disk.