PURPOSE: To increase the speed of printing operation by shortening the time required in one cycle at the access time of a memory by performing control so that image data are stored and the clearing of a memory region is not performed at a time when all of read image data are '0' when said image data are read from an image memory.

CONSTITUTION: A microprocessor 2 sends out a writing signal 3 to an image memory 7 when sends printing video data 15 to a printer unit 6 and subsequently reads the previously written printing data from the memory 7 according to the timing signal 8 from the printer unit 6 to further convert the same to video data 15 and performs send-out operation to the printer unit 6. At this time, a '0' data judge circuit 18 judges whether the read image data is '0' and, when said data is not '0', a memory clear signal 21 is supplied to the memory 7 to clear a reading data memory address and, when the read data is '0', the supply of the signal 21 to the memory 7 is not performed. By this method, a memory clear processing time can be shortened.