To provide a rotation supporting device whose load on a thrust bearing can be reduced for reducing electric power required for rotation drive even if the weight of a rotated object mounted to a cargo box is greater.

A motor 15 and a permanent magnet 16 are mounted to a fixed casing 14 fixed and arranged thereon. A thrust bearing 17 supports a load of a rotation side unit 12 in the thrusting direction. The cargo box 13 to which the rotated object 100 is mounted is mounted at the upper end of a rotating shaft 19. A ferromagnetic body 25 is arranged under the permanent magnet 16 in opposition to a magnetic pole surface 16a and mounted to a first rotation part 23 which is rotated together with the rotating shaft 19. A second rotation part 24 to which the first rotation part 23 is mounted and which is rotated together therewith is supported by the thrust bearing 17 and rotationally driven with the rotation of an output shaft 15a of the motor 15 transmitted thereto.

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