PURPOSE: To prevent the detecting accuracy by thermal expansion of fluid in a hot line from reducing by supplying the fluid from the outside to fluid pocket parts formed at upper and lower positions of a stator and a rotor through a fluid supply path and a flow rate limiter.

CONSTITUTION: Fluid 14 such as cooling liquid supplied from the outside through a fluid supply pipe 30 is supplied from a fluid supply port formed on an end plate to a fluid supply path 19 in the inside of the stator 12. After pressure is elevated by a fluid limiter 22 at fluid supply ports 20, 21, the fluid 14 is supplied to fluid pocket parts 15, 16 formed at upper and lower positions on the outside of the stator 12. Comparatively much fluid 14 elevated in pressure is supplied to the fluid pocket parts 15, 16, the fluid and pressure are restrained by a small gap 17 between the wall part 18 and the rotor 5 from escaping and the rotor 5 floats and is supported. Consequently, the fluid 14 can be prevented by the heat transmitted from a hot band plate 2 to the rotor 5 from thermally expanding remarkably.