An image forming apparatus comprising: a communication interface unit operable to perform communication with a cloud server that provides an application service; a user interface unit operable to display a screen and receive a user input; an image forming operation performing unit operable to perform an image forming operation; and a control unit, characterised by comprising a storage unit operable to store a plurality of databases that correspond to respective applications that are installed in the image forming apparatus; wherein the control unit is operable to store a plurality of pieces of user log-in information that match the applications, in the databases that correspond to the respective applications, so as to match the plurality of pieces of user log-in information with user accounts for the image forming apparatus, and to manage a log-in to a user account for the application by using the stored user log-in information. wherein the control unit comprises: a user log-in information managing unit operable to receive a token from the cloud server, to encrypt the token, and to store the encrypted token in the user log-in information that matches with the user account for the image forming apparatus, when the user, who logs into the user account for the image forming apparatus, logs into the user account for the application; and a log-in maintenance managing unit operable to maintain the log-in status to the user account for the application by periodically transmitting the token that is stored in the user log-in information to the cloud server. a communication interface unit operable to perform communication with a cloud server that provides an application service; a user interface unit operable to display a screen and receive a user input; an image forming operation performing unit operable to perform an image forming operation; and a control unit, characterised by comprising a storage unit operable to store a plurality of databases that correspond to respective applications that are installed in the image forming apparatus; wherein the control unit is operable to store a plurality of pieces of user log-in information that match the applications, in the databases that correspond to the respective applications, so as to match the plurality of pieces of user log-in information with user accounts for the image forming apparatus, and to manage a log-in to a user account for the application by using the stored user log-in information. wherein the control unit comprises: a user log-in information managing unit operable to receive a token from the cloud server, to encrypt the token, and to store the encrypted token in the user log-in information that matches with the user account for the image forming apparatus, when the user, who logs into the user account for the image forming apparatus, logs into the user account for the application; and a log-in maintenance managing unit operable to maintain the log-in status to the user account for the application by periodically transmitting the token that is stored in the user log-in information to the cloud server. a user log-in information managing unit operable to receive a token from the cloud server, to encrypt the token, and to store the encrypted token in the user log-in information that matches with the user account for the image forming apparatus, when the user, who logs into the user account for the image forming apparatus, logs into the user account for the application; and a log-in maintenance managing unit operable to maintain the log-in status to the user account for the application by periodically transmitting the token that is stored in the user log-in information to the cloud server.