To provide a method for authenticating a detachable cartridge and preventing the duplication and forgery of the detachable cartridge.

A technique for authenticating a headerless ID magnetic disk comprises a step 1000 for inserting the headerless ID magnetic disk provided with plural defect positions and a ciphered defect map into a detachable drive unit, a step 1010 for taking out the ciphered defect map from the magnetic disk, a step 1020 for storing the ciphered defect map inside a memory inside the detachable drive unit, the step for deciphering 1030 the ciphered defect map and forming a defect map for specifying the plural defect positions and a step for accessing a position other than the plural defect positions on the headerless ID magnetic disk by using the defect map inside the memory.