The object of the invention is to provide a storage device represented by a removable hard disk from which a cartridge having a storage medium is removable, to which cartridges having different specification sizes of the outer shapes can be applied. A cartridge of this invention is detachably loaded in a holder portion for a storage device outside a computer or a storage device incorporated in a computer, and has a storage medium. The cartridge includes a groove which engages with a locking portion provided to the holder portion to releasably lock the cartridge. The groove is formed at a predetermined distance in an inserting/removing direction from an end of the cartridge. This distance is set common for another cartridge which is detachably loaded in the holder portion and has a length different from that of the cartridge in the inserting/removing direction.