A disk device comprises first and second disk selection projections 102, 103 which regulate an angle of the disk conveyed to a small or large disk positioning recess 121, 122 on the basis of an outer radius of the disk. The first and second disk selection projections have tapered faces 102a, 103a provided at fixed intervals on a disk guiding face 101a facing the conveying roller 111. The disk device further comprises steps 121a, 122a for positioning the small disk 201 or the large disk 200 having an angle regulated in accordance with the outer radius to the small disk positioning recess 121 or to the large disk positioning recess 122.