An opposed interval between a pair of fore position regulating pieces forming a guide mechanism of the disk tray is made wider than the mutual interval between guide ways. The projecting width of the fore position regulating pieces is longer, its opposed interval being closer to the mutual interval between the guide ways. A front end portion of guide way is formed as an run-off guide way, the run-off guide way and the guide way being continuous on a nominal guide way. The open angle of the nominal guide way is decided in a range from 110.degree. to 135.degree..