IMAGE FORMING DEVICE

PURPOSE:To improve durability and image quality without changing the press- contacting force of a developing roller in the direction of a photosensitive body. CONSTITUTION:A motor 57 is attached to a developing case 51 and a crossed helical gear 59 attached to the shaft 52a of the developing roller 52 is driven via a worm gear 58. On the other hand, a motor 57 and a connecting plate for applying a developing bias 60 are electrically connected with a printer main body via a harness 61 and a connector 12. External force accompanying with driving does not act on a developing unit, so that fluctuations in a gap and the abnormal abrasion of a gap holding member can be prevented. Moreover, the removability of an image forming unit and a main body is improved, and a reduction ratio between the motor and a roller can be made high.