During print processing based on print data from host computer 100, if memory shortage occurs in RAM 16, information on the occurrence of memory shortage, memory-use status and the like is sent to the host computer 100. The host computer 100 receives the information and allocates a storage area in the RAM 3 based on the information. Form information and the like, registered in the RAM 16 are transferred to the host computer and saved in the allocated storage area, thus expanding an available area of the RAM 16 for printing. When the print processing has been completed, the completion of printing is notified to the host computer 100, so that the saved information is transferred from the host computer 100, and stored into the RAM 16.