An image forming apparatus includes an image forming unit and a control unit. The image forming unit forms a test image based on test image data. The test image data includes a first image area and a second image area. The first image area is disposed adjacent to the second image area. The first image area is an image area including a mixed color image of a first primary color and a second primary color and has the same gradation value in a main scanning direction. The second image area is an image area of the second primary color and has the same gradation value in the main scanning direction. The control unit corrects a correction table based on the test image formed in the image forming unit. In the correction table, for each primary color, the gradation value is corrected according to a position in the main scanning direction.