To improve the performance and the reliability by preventing the buckling of bellows.

This rotation control structure for braking the rotation of a rotor 10 is provided with the bellows 20 having an air suction and discharge port 26a for sucking the external air inside in expanding of a main body part 21, and discharging the air in the main body part 21 to the external in compression, the bellow main body part 21 is mounted on a base 1 and the rotor 10 in a state that an expanding amount on the inner face 20a side located on the pivot shaft 8 side is les than that on the opposite outer face 20b side, and curved into the bow shape corresponding to the rotating locus S of the rotor 10, whereby the bellows can be expanded and contracted approximately along the rotating locus S of the rotor 10.