A procedure for login in a case where a prescribed job is executed in an image processor is simplified. An image processor includes: input unit accepting an input of user authentication information from a user; user authentication unit performing user authentication by comparing the inputted user authentication information with the stored user authentication information to authorize execution of processing; and temporary ID generation unit generating an temporary ID if the user authentication is successful to store the temporary ID, being related to the user authentication information, wherein the input unit accepts an input of the temporary ID and the user authentication unit compares the inputted temporary ID with the stored temporary ID to thereby perform the user authentication and to authorize execution of the processing.