A printing device capable of preventing a printing process from being performed in accordance with print information sent from a printer driver in version for which permission of use is not given. In a host computer, a print data generator adds signature data to print data, which is transferred to a printer, by employing a signature algorithm and signature-related data. In a printer, a print data analyzing/processing unit extracts the signature data having been added to the print data transferred from the host computer, and verifies the extracted signature by employing a signature verification algorithm and signature verification data.