PURPOSE: To simplify a structure and to reduce cost by applying wet steam flowing from an exhaust port at a high-pressure stage to a high speed centrifugal separator to separate water and obtain dried steam, supplying the dried steam to a low-pressure stage side, and supplying the steam containing the separated water to a reheater.

CONSTITUTION: A high-pressure stage 1 of a steam expansion turbine has two sets of wet steam exhaust ports 2, 4 and 3, 5, and they are connected with low-pressure stages 34, 36, 38 arranged on the same axis as the high-pressure stage 1 through main conduits 20 and 21, respectively. The main conduits 20, 21 are constituted such that pipes 22 to 27 branched per low-pressure stage are provided with separators and heaters 28 to 33, respectively, so that a stream of steam is overheated and/or dried. In this case, high speed centrifugal separators 40, 41 which correspond to each exhaust port 2 to 7 and receive the steam exhausted from the high-pressure stage 1 are provided to feed the dried steam obtained in the centrifugal separators 40, 41 to a low-pressure stage side, and the extracted wet steam is fed to steam reheaters 22A, 23A through pipes 6, 7 and high speed auxiliary centrifugal separators 6A, 7A and pipes 18, 19.