To prevent forgery of printouts by a simple configuration that can be easily introduced to an existing system, a printer 3 that prints a receipt based on print data sent from a POS terminal 2 has: a code generating unit 33 that generates a unique code unique to each receipt based on the print data; a print control unit 31 and print unit 45 that print a receipt based on the print data, and print the unique code on the receipt; and a code transmission unit 34 that outputs the unique code to a receipt history server 6.