A steam turbine plant includes a steam turbine with a shrink-fit type rotor and a gland seal steam supply apparatus that supplies gland seal steam into the gland portion of the steam turbine. The gland seal steam supply apparatus has an evaporator that uses main steam or turbine extraction steam as a heating medium. A steam supply apparatus supplies steam generated within the evaporator into the portions of the turbine which are in danger of developing stress corrosion cracks. The steam supply apparatus includes a pressure reducing apparatus for supplying steam at a reduced pressure into the portions which are in danger of developing stress corrosion cracks. A steam detecting apparatus detects the steam conditions in the rotor as a function of the turbine load and a control apparatus receives the detected signal from the steam detecting apparatus for the purpose of controlling either the pressure of steam generated within the evaporator or the operation of the pressure reducing apparatus.