PURPOSE: To reduce a load of a CPU by grasping a quantity of a data supplied to a data processing device, by a data supply device side, and varying an issue period of a polling signal after a processing data has been supplied, in accordance with whether the data quantity is large or small.

CONSTITUTION: By a printing start command, a printer control part 3 reads out successively a printing data stored in a work area 21 on a main memory 2, by a prescribed unit by a DMA, etc., and supplies it to a printer 4. A CPU1 generates a command, and thereafter, sets a corresponding time counting time to a timer 12 by expecting a time when a printing processing to the number of characters counted by a character number counter 11 would be ended. When the time to which the timer 12 has been set is counted, a time-up signal UP is outputted to a polling indicating part 13. By this time-up signal UP, a polling indicating command is generated to the printer control part 3 from the polling indicating part 13.