PURPOSE: To obtain excellent erecting characteristics even when a slant angle is a minute angle, by filling a part of the ring shaped cavity of a rotary container, which is rotated at a low speed by a motor that is attached to a base table, with a working fluid.

CONSTITUTION: A central hole 3-26' of a disc part 3-26 of a rotary container 3- 25, which is contacted with a flange 3-23" and has a ring shaped cavity part 3- 24 at the outside, is coupled to a shaft 3-23. The upper end of the shaft is linked to a driving shaft 3-29 of a motor 3-28 having a built-in speed reducing mechanism through a coupling 3-27. The inside of the cavity part 3-24 of the rotary container 3-25 contains a high-viscosity working fluid 3-30 so that one half of the container is filled.