An image forming apparatus including an image bearing member, a charger, an irradiator, and a developing device, wherein the relationships T1≦T2 and T2=W/V are satisfied, wherein T1 (msec) represents a real transit time, defined as a value on X-axis of a first flection point, at which a surface potential (Y) of the image bearing member firstly rises up when a time (X) between irradiating the image bearing member and measuring the surface potential of the irradiated portion thereof is shortened, in a graph showing a relationship between X and Y; T2 (msec) represents a charging time; W (mm) represents a charging width of the charger; and V (mm/msec) represents a linear velocity of the image bearing member.