An image forming apparatus includes: a power source applying voltage to a charging roller to charge a photosensitive drum; a toner-image forming unit forming a toner image on the photosensitive drum; a detecting member which detects a DC current to be flowed from the charging roller to the photosensitive drum; a driving source driving the photosensitive drum at a predetermined speed; and an execution unit executing a detection mode to detect the DC current with the detecting member when the voltage is applied in a state in which the photosensitive drum is rotated, in a period except a period during which the toner image is formed on the photosensitive drum, the execution unit setting a speed of the driving source when the detection mode is executed at a second speed faster than a first speed that is fastest in the period during which the toner image is formed.