When a content is moved from a flash memory into a content database, a usage rule management program updates a variable seq-1, stored in a 0th defective block of a media defect list stored in the flash memory, to a new value seq-2. The usage rule management program calculates an MAC value (hash value) on the basis of the content stored in the data portion of the flash memory, an encrypted encryption key, and important information including the variable seq#. The usage rule management program then compares the calculated value with an MAC value stored in the header portion of the flash memory. If these two values are not equal, the usage rule management program disables reproduction of the content thereby preventing the content from being copied in an unauthorized manner.