Image forming apparatus capable of suppressing generation of streak image without complicating configuration, and adjustment method

An image forming apparatus, comprising:

• a first ejection portion which includes a plurality of first nozzles arranged along a width direction orthogonal to a conveying direction of a sheet, and causes ink to be ejected from each of the first nozzles;
• a second ejection portion which includes a plurality of second nozzles arranged along the width direction, some of the plurality of second nozzles being arranged so as to overlap with some of the plurality of first nozzles in the width direction at a position that is more on a specific direction side along the width direction than the first ejection portion, and causes the ink to be ejected from each of the second nozzles;
• an acquisition processing portion which acquires a first separation distance between a third nozzle and a fourth nozzle in the width direction, the third nozzle being included in an overlapping portion of the plurality of first nozzles with the plurality of second nozzles, the fourth nozzle being closest to the third nozzle out of the second nozzles positioned more on the specific direction side than the third nozzle;
• a first setting processing portion which sets, when the first separation distance acquired by the acquisition processing portion is equal to or larger than a predetermined threshold value, the second nozzles positioned on the specific direction side from the fourth nozzle out of the plurality of second nozzles as a usage area to be used for ejecting the ink, and sets, when the first separation distance is smaller than the threshold value, the second nozzles positioned on the specific direction side from a fifth nozzle adjacent to the fourth nozzle on the specific direction side of the fourth nozzle out of the plurality of second nozzles as the usage area;
• and
• an adjustment processing portion which decreases, when the first separation distance acquired by the acquisition processing portion is equal to or larger than the threshold value, an ejection amount of the ink of either one or both of the third nozzle and the fourth nozzle based on the first separation distance, and increases, when the first separation distance is smaller than the threshold value, the ejection amount of the ink of either one or both of the third nozzle and the fifth nozzle based on a second separation distance between the third nozzle and the fifth nozzle in the width direction.