A printer can be connected to a computer or other host device without being limited by the type of data processed by the printer. A POS system 1 has a POS terminal 10 connected to a first printer 60 that has a print unit 71. The print data acquisition unit 66 of the first printer 60 acquires data output by the POS terminal 10. A conversion unit 67 applies at least one of a process of converting graphic data to text data, and a process of converting text data to graphic data, to the data acquired by the data acquisition unit 66, and the conversion unit 67 outputs the resulting converted data.