A PJL processing program for executing a process corresponding to a PJL command received from the host includes a command option recognizing program for recognizing the PJL command, the option dictionary for storing the information name (option name) which is capable of corresponding to a request by the PJL command and associated with the location of the corresponding information, and an option executing program for executing a process corresponding to the request when the information of the requested object exists in the option dictionary. The option dictionary is stored in the flash ROM while the command option recognizing program and the option executing program, which have little possibility to be changed, are stored in the mask ROM.