In a belt continuously-variable transmission, a casing or a housing is formed with an air communicating hole extending through an upper part of the casing or the housing. In this invention, in an image processing system in which a computer and a plurality of printers are connected via a serial bus, the computer acquires printer device information and efficiently acquires channels for isochronous transfer on the serial bus on the basis of whether channels can be shared by image data of a plurality of colors to be transferred to the printer. Starting from a meso-diol, optically pure compounds were prepared without utilizing chiral ligands at any stage of the synthesis.