When encryption processing means is decided in encryption print communication which is made between a PC and a printer, a transmission/reception control unit of a printer receives information of encryption processing means from the PC and stores into a list storing unit of a RAM. A list of encryption processing means which are used in the printer is read out from a flash memory. An upper apparatus encryption processing means list is compared with the encryption processing means list. If the coincident encryption processing means exists, it is decided that this means is used for communication and the PC is notified of it. Since the PC transmits the print data encrypted by the notified encryption processing means to the control unit, the printing is executed on the basis of the decrypted print data.