A data using device that executes a predetermined process by using data, comprising: a data storage part that stores pieces of data used for the predetermined process; a user storage part that stores a first user identification information; an authentication data acquisition part that acquires, from an external apparatus, authentication data that is data requiring authentication using the first user identification information when using the authentication data for the predetermined process; a user acquisition part that acquires a second user identification information indicating a user who can use the authentication data acquired by the authentication data acquisition part from the external apparatus; and a user determination part that determines whether the second user identification information acquired by the user acquisition part matches the first user identification information stored in the user storage part; the data using device being characterized in further comprising: an authentication storage processing part that stores the authentication data acquired by the authentication data acquisition part into the data storage part such that the authentication data is available for the predetermined process in a case where the first user identification information is not stored in the user storage part; and a) a user deletion part that deletes the first user identification information stored in the user storage part or instructs a user to delete the first user identification information in a case where the user determination part determines that the first and second user identification information do not match each other; and a data use prohibition part that prohibits use of the authentication data stored in the data storage part in a case where the first user identification information stored in the user storage part is deleted and/or b) a user setting part that stores the second user identification information acquired by the user acquisition part into the user storage part in a case where the authentication data is stored into the data storage part by the authentication storage processing part in a state in which the first user identification information is not stored in the user storage part. a data storage part that stores pieces of data used for the predetermined process; a user storage part that stores a first user identification information; an authentication data acquisition part that acquires, from an external apparatus, authentication data that is data requiring authentication using the first user identification information when using the authentication data for the predetermined process; a user acquisition part that acquires a second user identification information indicating a user who can use the authentication data acquired by the authentication data acquisition part from the external apparatus; and a user determination part that determines whether the second user identification information acquired by the user acquisition part matches the first user identification information stored in the user storage part; the data using device being characterized in further comprising: an authentication storage processing part that stores the authentication data acquired by the authentication data acquisition part into the data storage part such that the authentication data is available for the predetermined process in a case where the first user identification information is not stored in the user storage part; and a) a user deletion part that deletes the first user identification information stored in the user storage part or instructs a user to delete the first user identification information in a case where the user determination part determines that the first and second user identification information do not match each other; and a data use prohibition part that prohibits use of the authentication data stored in the data storage part in a case where the first user identification information stored in the user storage part is deleted and/or b) a user setting part that stores the second user identification information acquired by the user acquisition part into the user storage part in a case where the authentication data is stored into the data storage part by the authentication storage processing part in a state in which the first user identification information is not stored in the user storage part. a) a user deletion part that deletes the first user identification information stored in the user storage part or instructs a user to delete the first user identification information in a case where the user determination part determines that the first and second user identification information do not match each other; and a data use prohibition part that prohibits use of the authentication data stored in the data storage part in a case where the first user identification information stored in the user storage part is deleted and/or b) a user setting part that stores the second user identification information acquired by the user acquisition part into the user storage part in a case where the authentication data is stored into the data storage part by the authentication storage processing part in a state in which the first user identification information is not stored in the user storage part.