One embodiment of the present invention is connected to a drive source, movable with the first member to be moved in the circumferential direction about the predetermined axis by the driving force from the drive source, in the circumferential direction about the predetermined axis in, and a second member which is arranged so as to be located on the peripheral direction of the movement locus of the first member, is disposed between the first member and the second member, at least a second member contacting the, the covering member having flexibility, provided on the covering member, a driving force transmission mechanism and a index indicating the state change of the contact surface between the second member in the covering member
