the photosensitive drum however the contact pressures are different from each other at the four contact portions and the amounts of roller deformation are also different from each other at the four contact portions each roller is deformed in the amount of 100 u03bcm under pressure of 1 kgf in this case the contact pressures at the upper front side contact portion and the lower rear side contact portion are 0 5 kgf and the contact pressures at the upper rear side contact portion and the lower front side contact portion are 1 5 kgf in the case where the contact pressures at the four contact portions are equal to each other the deformation amount is 100 u03bcm and therefore the nominal sd gap during the urging is smaller than that before the urging by 100 u03bcm finally the sd gap is on the basis of the nominal value during the urging 50 u03bcm at the upper front side u00b1 0 u03bcm at the upper central portion u2212 50 u03bcm at the upper rear side u2212 50 u03bcm at the lower front side u00b1 0 u03bcm at the lower central portion and 50 u03bcm at the lower rear side in the case of the constitution in this embodiment before the urging by the urging unit 21 the position of the developing device 14 is not determined by the urging the developing device 14 is slightly rotated in the b direction until the contact pressures at the upper rear side.