The disclosure discloses a printer including a memory that stores reference information indicating a reference setting state in relation to at least one operation setting item in relation to the printed matter production process by using a print-receiving medium, to be non-rewritable. When computer-executable instructions stored in memory executed by a processor, the printer to perform a difference information generation process and a difference information output process. In the difference information generation process, difference information is generated. The difference information indicates a difference of a setting state in relation to the at least one operation setting item at a predetermined timing determined in advance, from the reference setting state. In the difference information output process, the difference information generated in the difference information generation process is outputted to an exterior of the printer.