To improve heating efficiency by smoothly controlling supply/discharge of a fluid to/from the inside of a hollow rotating shaft, and circulation of the fluid between the hollow rotating shaft and a disc blade.

A plurality of pipes 11 communicating between an internal space 8 of a hollow rotating shaft 3 and an internal space 9 of a disc blade 4 are arranged at intervals in a circumferential direction for each disc blade 4 in a state of being opened to an outer peripheral face of the hollow rotating shaft 3 and projecting inward in the radial direction of the hollow rotating shaft 3. A partitioning plate is disposed in the disc blade 4 while radially extending from a rear position in the rotating direction, of pipe openings 43 of at least a part of the pipes 11 to partition the internal space 9 of the disc blade 4. A drain discharge pipe 6 is supported by the hollow rotating shaft 3 through a rotary joint 7, an end portion in the hollow rotating shaft 3, of the drain discharge pipe 6 is directed downward, and its lower end opening 6a faces an inner peripheral face of the hollow rotating shaft 3.