PURPOSE: To provide the back exposure developing method which can form a sharp image even on a photosensitive body using, specially, a-Si by eliminating a ghost phenomenon, a fog, etc., due to an abrupt increase in the developer resistance in a low-electric-field area.

CONSTITUTION: Even when a developer deteriorates as a result of the repetition of the contact electrostatic charging and exposure of the photosensitive body and a toner rubbing area 10, development can be performed within a range wherein the developer resistance after the deterioration satisfies Rt < (Vc/ Vs-Vc)Rh. In the inequality, Rt is the developer resistance (when a developable voltage Vc is applied), Vs a developing bias (voltage) applied to a developer carrier, Vc the developable voltage, and Rh the bright resistance of the photosensitive body.