A method of setting function, comprising: a first step of connecting a first recording medium to a first electrical apparatus having an optional function either disabled or temporarily enabled, the first recording medium containing license information to enable the optional function; a second step of allowing the first electrical apparatus to authenticate the license information; a third step, subsequent to the second step, of enabling the optional function of the first electrical apparatus; a fourth step, subsequent to the third step, of recording the optional function as having been authenticated in the license information; a fifth step, subsequent to the fourth step, of connecting a second recording medium to the first electrical apparatus, the second recording medium being different from the first recording medium; a sixth step (2-3, 2-4), subsequent to the fifth step, of disabling the optional function of the first electrical apparatus; and a seventh step, subsequent to the sixth step, of recording the optional function in the second recording medium as being authenticable in the license information, wherein, in the second step, the first electrical apparatus verifies individual identification information that is unique to the first recording medium and is recorded in a memory region of the recording medium containing data that is written by the manufacturer and can only be read by a user by comparing it with media identification information that indicates which recording medium license information belongs to and is stored in memory region of the recording medium containing data that can be read and written by the user and contained in the license information, in the third step, the first electrical apparatus stores a serial number of the optional function stored in the first recording medium; and in the sixth step, the serial number stored in the first electrical apparatus is recorded in the second recording medium. a first step of connecting a first recording medium to a first electrical apparatus having an optional function either disabled or temporarily enabled, the first recording medium containing license information to enable the optional function; a second step of allowing the first electrical apparatus to authenticate the license information; a third step, subsequent to the second step, of enabling the optional function of the first electrical apparatus; a fourth step, subsequent to the third step, of recording the optional function as having been authenticated in the license information; a fifth step, subsequent to the fourth step, of connecting a second recording medium to the first electrical apparatus, the second recording medium being different from the first recording medium; a sixth step (2-3, 2-4), subsequent to the fifth step, of disabling the optional function of the first electrical apparatus; and a seventh step, subsequent to the sixth step, of recording the optional function in the second recording medium as being authenticable in the license information, wherein, in the second step, the first electrical apparatus verifies individual identification information that is unique to the first recording medium and is recorded in a memory region of the recording medium containing data that is written by the manufacturer and can only be read by a user by comparing it with media identification information that indicates which recording medium license information belongs to and is stored in memory region of the recording medium containing data that can be read and written by the user and contained in the license information, in the third step, the first electrical apparatus stores a serial number of the optional function stored in the first recording medium; and in the sixth step, the serial number stored in the first electrical apparatus is recorded in the second recording medium.