1. A control device of a marking device comprising dividing process means for receiving and dividing data of an original image (18) into a plurality of divided images (19), display means for performing sequential switching display of each divided image (19) on a display screen (10) of a liquid-crystal mask (6), drive control means for driving and controlling actuators (12, 16) so as to change to a corresponding irradiation position (17a) on a work (17) each time switching display of the divided image (19) is performed to thereby mark a pattern (ABCDE) of the original image (18) on the work (17), the dividing process means being constructed and arranged for sequentially scanning each line of the original image (18) and judging for each line whether all pixels are a logical "0" corresponding to a "background" or are a logical "1" corresponding to a "pattern" thereby determining a minimum rectangle that circumscribes the pattern (ABCDE) or respective minimum rectangles (22, 23); (29, 28, 23), respectively, that circumscribe respective patterns (ABC), (DE); (AB), (C) and (DE), respectively, which are separated patterns of the pattern (ABCDE) and to determine coordinate positions (P1, P2 and P3) of the circumscribed minimum rectangles (22, 23); (29, 28, 23), respectively, on the original image (18) thereby generating the divided image (19) only for the circumscribed minimum rectangles (22, 23); (29, 28, 23), respectively, (FIGS. 6, 7, 9-11), the display means displays in the sequentially changing manner the divided image (19) generated only for the circumscribed minimum rectangles (22, 23); (29, 28, 23), respectively, on the display screen (10) of the liquid-crystal mask (6), and the drive control means, on the basis of the coordinate positions (P1, P2 and P3) of the circumscribed minimum rectangles (22, 23); (29, 28, 23), respectively, on the original image (18) drives and controls the actuators (12, 16) so as to change to the corresponding irradiation position (17a) on the work (17) each time switching display of the divided image (19) is performed to thereby mark the pattern (ABCDE) of the original image (18) on the work (17).