An image forming apparatus including: a photosensitive member; a conveying member; an exposure head; a developing unit; an image forming unit; a concentration sensor having a first detection width in a conveyance direction and a second detection width in an axial direction of the photosensitive member; and a control unit, wherein the control unit controls the exposure head and the image forming unit to form a first image for correction, which includes a straight line part extending in the axial direction of the photosensitive member and having a length equal to or larger than the second detection width of the concentration sensor, on the conveying member, and wherein the control unit corrects a developing bias to be applied to the developing unit based on a detection result of the first image for correction by the concentration sensor.