Disclosed is a method of verifying a number of media in a media storage unit, the method including: while retrieving a medium from a media storage unit and moving the medium, recognizing, by a discriminating unit, a serial number of the medium; comparing the serial number of the medium recognized by the discriminating unit with a record of a database in which serial numbers of media stored in the media storage unit are recorded, and searching for whether there is a serial number that matches the recognized serial number of the medium; and when a result of the searching is that the matching serial number is found, deleting data of the medium corresponding to the matching serial number and data of an upper medium of the medium recorded on the database, and based on data of lower media that remain after the deleting, updating the record of the database regarding a number of the media stored in the corresponding media storage unit.