A computer (2) connected to a printer (1) stores a printer sharing control program (50) for creating print spool files and sending the print spool files to the printer in response to print requests received from a plurality of printer use programs (40). The printer sharing control program (50) generates an interrupt printing control function (56) for storing interrupt printing condition information set to each print request source, a temporary storage function (54) for temporarily storing the print spool files for distinguishing the print request sources, and a data processing function (52) for sending a priority print spool file to the printer based on said interrupt printing condition information.