To provide an information processor for appropriately executing the failure demarcation and media exchange of a magneto-optical disk autochanger.

When an access error occurs, a media management controller 111 allows the disk driver device to re-try access using another magneto-optical disk. When the error is escaped, the media management controller 111 informs an information processor 10 main body that the magneto-optical disk is the cause of the error. On the other hand, when the error can not be escaped, the media management controller 111 allows another disk driver device to re-try access using the magneto-optical disk which is driven when the error occurs. When the error is escaped by this re-try, the media management controller 111 informs the information processor 10 main body that the disk drive device is the cause of the error.