PURPOSE: To provide a cartridge for a disk device, which can suppress the generation of abrasion powder utmost and to propose the structure of a window part for head access, wherein abrasion dusting is less.

CONSTITUTION: A cartridge 4 for a disk device rotatably contains a disk-shaped recording medium 1 in the inside and comprises a pair of upper and lower half cases 2 and 3. Thin parts 6 are provided along the entire widths of the upper surface of the upper half case and the lower surface of the lower half case in the direction perpendicular to the cartridge inserting direction (a) to the main body of the device. Notched parts 19 are provided at both side-surface parts of the cartridge corresponding to the thin parts.