An image forming apparatus includes a photosensitive drum life estimation mechanism which estimates wear amounts of a charge transfer layer in both of a toner bearing area and an end portion of a toner non-bearing area of a developing roller and informs a user that the photosensitive drum has reached the end of its life if, out of total wear amounts of the areas corresponding to predetermined life threshold values of the toner bearing and non-bearing areas, either of the total wear amounts reaches the threshold value.