PURPOSE: To record a high-grade image without lowering the speed of an image forming process by allotting the dot group corresponding to the n-th image of a multivalue image to each of a plurality of scannings and allotting the respective dots of one dot group to a plurality of scannings to form an image.

CONSTITUTION: Dot data of the first and second values 1, 2 are recorded by the first scanning and dot data of the second and third values 2, 3 are recorded by the second scanning. As a result, a recording image composed of one pixel formed from three dots shown by 1-3 in a main scanning direction is obtained. At this time, in the first scanning, lower 128 of 256 nozzles of each color head of an ink jet head 56 are used to perform recording using 128 dots and, in the second scanning, 128 upper half nozzles of the ink jet head are used to perform recording using 128 dots.