A printout apparatus for performing printing that involves authentication and being capable of communication with an external terminal and with an authentication server, comprising: communication means for receiving, from an external terminal, authentication information required for user authentication in printing that involves the authentication; acquisition means for acquiring transmission-source user identification information for identifying a transmission source user of the authentication information at the time of reception of the authentication information, wherein the transmission-source user identification information is information for identifying a user who has transmitted the authentication information; registration processing means for registering the transmission-source user identification information and the authentication information in association with each other in the printout apparatus when the authentication information has been received from the external terminal and the transmission-source user identification information has been acquired, the communication means further being adapted for receiving a print job from the external terminal at a time subsequent to a time of reception of the authentication information, the acquisition means further being adapted for acquiring client user identification information for identifying a client user of the print job when the print job is received from the external terminal, wherein the client user information is information for identifying a user who has requested the print job, whereby the printout apparatus is configured to determine, on the basis of the transmission-source user identification information and the client user identification information, whether or not the transmission-source user is the same as the client user; and the printout apparatus further comprising identification means for identifying, when the transmission source user and the client user are determined to be the same on the basis of the transmission-source user identification information registered in the printout apparatus and the client user identification information acquired at the time of reception of the print job, the authentication information received from the external terminal that is associated with the transmission-source user identification information registered in the printout apparatus as information to be used for the user authentication in the authentication server, the communication means further being adapted for transmitting the authentication information to the authentication server and for receiving an authentication result from the authentication server, the printout apparatus further comprising job control means for executing the print job when the user authentication that is executed using the authentication information identified by the identification means has succeeded. communication means for receiving, from an external terminal, authentication information required for user authentication in printing that involves the authentication; acquisition means for acquiring transmission-source user identification information for identifying a transmission source user of the authentication information at the time of reception of the authentication information, wherein the transmission-source user identification information is information for identifying a user who has transmitted the authentication information; registration processing means for registering the transmission-source user identification information and the authentication information in association with each other in the printout apparatus when the authentication information has been received from the external terminal and the transmission-source user identification information has been acquired, the communication means further being adapted for receiving a print job from the external terminal at a time subsequent to a time of reception of the authentication information, the acquisition means further being adapted for acquiring client user identification information for identifying a client user of the print job when the print job is received from the external terminal, wherein the client user information is information for identifying a user who has requested the print job, whereby the printout apparatus is configured to determine, on the basis of the transmission-source user identification information and the client user identification information, whether or not the transmission-source user is the same as the client user; and the printout apparatus further comprising identification means for identifying, when the transmission source user and the client user are determined to be the same on the basis of the transmission-source user identification information registered in the printout apparatus and the client user identification information acquired at the time of reception of the print job, the authentication information received from the external terminal that is associated with the transmission-source user identification information registered in the printout apparatus as information to be used for the user authentication in the authentication server, the communication means further being adapted for transmitting the authentication information to the authentication server and for receiving an authentication result from the authentication server, the printout apparatus further comprising job control means for executing the print job when the user authentication that is executed using the authentication information identified by the identification means has succeeded.