To provide an image forming position adjuster and its adjusting method by which an X direction positional deviation, a Y direction positional deviation and the inclining positional deviation of a main scanning direction are detected at a time.

Pattern data for visual observation 51 and 52 are prepared in a memory. The pattern data 51 have a rectangular outside frame constituted of sides in parallel with each other in longitudinal and lateral directions, and a predetermined area within a frame (whole area in this instance) is constituted of dot data to be painted out in black. The pattern data 52 have a step wise shape for each dot in the longitudinal and lateral directions, and the predetermined area inside of the outside frame (whole area in this instance) is constituted of the dot data to be painted out in cyan, magenta or yellow so as to align a maximum projecting part with the outside frame 53 of the pattern data 51. A test pattern 54 is formed by printing after superposing the black image pattern 51 and the color image pattern 52 at the same position. The positional deviation is easily known by counting the steps of the step wise color image pattern 52 projecting from the black image pattern 51.