1. An image forming device which is arranged to execute an authentication print job being a print job in which a user authentication is performed using a predetermined authentication device and a start of execution of a printout process is determined based on a result of the user authentication, comprising: a communication interface that is arranged to receive print data related to a print job; a non-transitory computer readable memory that is arranged to hold job data for an authentication print job based on the print data; a job execution unit that is arranged to execute a job based on the job data; an authentication unit that is the predetermined authentication device; a user authentication unit that is arranged to output a result of the user authentication using said authentication unit; a control unit that is arranged to control operations of said job execution unit so as to instruct a start of execution of the authentication print job to said job execution unit based on the user authentication result outputted by said user authentication unit; and an instruction generation unit that is arranged to determine content of a changing instruction for a setting being set with respect to the authentication print job based on an input of a user authentication result and output to said control unit the determined content of the changing instruction, wherein: said instruction generation unit determines the content of the changing instruction for the setting with respect to at least one authentication print job in at least one of an execution state and an execution queuing state based on the input of the user authentication result that is received in an after user authentication period being a period in which the at least one authentication print job of the user who relates to the input of the user authentication result is in at least one of the execution state and the execution queuing state at said job execution unit and outputs to said control unit the determined content of the changing instruction; said control unit executes a process of changing the setting with respect to the authentication print job based on the changing instruction; and the changing instruction is an instruction to change a setting for increasing a value of a number of sets of prints of a document with respect to the authentication print job in the execution state by a first print value equal to a value obtained by multiplying a first predetermined value, being a natural number, to a number of inputs of the user authentication result that is received in the after user authentication period.