PURPOSE: To perform printing processing corresponding to an extended or added control command by down-loading the added or extended control command which can not be analyzed by a printing device to the printing device in advance.

CONSTITUTION: A CPU 6 decides whether or not the control command received from a host computer 1 is a down-load command for down-loading a specific command. According to the decision result, the specific command is down-loaded and compared with a command which is already down-loaded. According to the comparison result, the specific down-loaded command is registered or discarded. Then it is decided whether or not the specific registered command is an extended/added command for extending or adding a processing function. Print information received on the basis of the decision result is processed according to the registered extended/added command. Therefore, the print information can accurately be processed on the basis of the extended or added control command.