The present invention provides a method and apparatus for using hot gas to defrost sequentially each refrigerated display case in a group of refrigerated display cases. The rotatable roller has an axis of rotation extending transversely to a direction of advancement of the attachment device or vacuum cleaner. A plurality of magnets are mounted on an inner peripheral surface of the flywheel so as to rotate therewith. A detecting unit determines the duration of the control signal generated from the user input, and the playback image generating unit adjusts a specified speed of switching among a plurality of playback images according to the input of the control signal and the specified speed of switching playback images is adjusted according to the detected duration. The ligand contains a ring, particularly a phenyl group, or a hydrocarbon group which links an amino group and PR1R2, NR1R2, OR1, SR1, or AsR1R2 group such that the structure of the ligand can be stabilized. The mounting holes serve to couple to a wiper arm of a vehicle for driving reciprocal motion of the windshield wiper.