A grasping device for a bead ring grasps the bead ring formed of a wire wound around an annular winding unit provided on the outer circumferential surface of a rotary body while fixing a beginning and a termination of the wire. The imaging optical system of the reflective scanning optical system includes a curved mirror with a rotationally symmetrical reflecting surface and a lens having an anamorphic lens surface configuration on its one side. Stressors are coupled to the cabinet and positioned for operation to create a conditioned charge in the container. First, by turning on a first switch, a feedback loop is formed by the differential amplification circuit, the current generation circuit and the capacitor to perform a level shift, and the voltage charged in the capacitor is held by the holding circuit.