An image forming apparatus includes a plurality of image carrier units and a position determining unit. The image carrier units form toner images in a sequential manner, and each of the plurality of image carrier units includes an image carrier and a supporting member to support the image carrier. The position determining unit includes a holding member having a plurality of openings for receiving the supporting members of the respective image carriers and a pressure mechanism. Each of the plurality of openings has a predetermined shape to sustain a weight of a corresponding one of the plurality of image carrier units through a corresponding one of the supporting members in a vertical direction and to grip the corresponding one of the supporting members in a horizontal direction. The pressure mechanism presses the supporting members held through the plurality of openings of the holding member to fix the image carriers at respective specific positions.