A general-purpose computer cross-authenticates an external storage medium which is detachably loaded in the general-purpose computer, directly storing copyrighted data from its internal storage means into the loaded external storage medium. An HDD, an internal storage means of the general-purpose computer, holds such data protected by copyright as music data. A memory card driver directly cross-authenticates a memory card, which is an external storage medium, and, upon successful cross-authentication, controls the memory card so that it stores the data from the HDD.