A plurality of recording heads capable of ejecting inks of different colors is reciprocated relative to a recording material to print ink dots on the recording material while effecting main scanning in the forward and the backward pass thereof. A plurality of thinning patterns produced by preparing m x n unit picture element groups and arraying these unit groups in such a manner that the groups avoid mutually adjoining and assume a mutually complementary relation is used to effect a plurality of rounds of main scanning in the forward and the backward pass over an area which can be printed by one round of main scanning, record a thinned image, and complete the recording of an image. The array of picture element groups in the thinning patterns is determined so that the groups may mutually adjoin relative to the direction of main scanning. <IMAGE>
