To accurately chuck a disk and to miniaturize a mechanism by providing an MD positioning inserting pin and an MD shutter opening/closing mechanism in a tray for taking in/out a CD or an MD.

A CD is positioned by fitting and loading an 8cm diameter CD 8 or a 12cm diameter CD 9 onto its CD step 2 or CD step 3. An MD is preferably, loaded on a tray 1 by matching an insert direction indication mark 11 with an MD placing direction indication mark 7, both being described in the MD 10 main body. By fitting the MD 10 to an MD step 4 and inserting an MD positioning inserting pin 6 into a positioning hole in the MD bottom surface, not only the MD 10 and the tray 1 are accurately positioned but also placing in a mistaken state is prevented by matching with the insert direction indication mark 7.