Rotary body 22 is provided with storing hole 22E, 22F in two positions point-symmetrical to the rotational center at the upper part of flange 22C, and retainers 26, 27 having steel balls 25A, 25B, steel ball receiving holes 26A, 27A, coil springs 28A, 28B are stored therein from the opening side in order, and steel ball receiving hole 26A of one retainer 26 is provided with a tolerance that enables steel ball 25A to slightly move in the horizontal direction, and click plate 24 on which steel balls 25A, 25B are resiliently contacted is disposed between rotary body 22 and bearing 23, and as a result, it is possible to maintain rhythmical clicking and clicking sound even in case of repeating the rotating operation.