INK JET IMAGE FORMING DEVICE

PROBLEM TO BE SOLVED: To perform monochromatic printing at a speed higher than at full color printing by printing in a state that a printing head of the same color is arranged in a deviated manner in a monochrome mode. SOLUTION: A black printing head 101a, a cyan printing head 101b, magenta printing head 101c, and a yellow printing head 101d are arranged in sequence from left to right in the moving direction of a head carriage. At this time, only the black printing head 101a is arranged being deviated upward from other printing heads 101. That is, the lower end of a nozzle row 102 of the black printing head 101a is arranged so as to nearly coincide with the top end of a nozzle row 102 of the cyan printing head 101b. When the cyan printing head 101b is changed to the black printing head, in a case that the head carriage is scanned in the direction of arrow X, printing can be done at a doubled width in the vertical direction. That is, even when the moving speed of the head carriage is the same as in the case of conventional full color printing, printing can be done at a speed twice as high as a conventional speed at the time of black printing.