Patent ID: 8116647

Claim:
An image forming apparatus comprising: a photoconductive drum; a developing roller opposite the photoconductive drum with a gap secured in between, and carrying toner that is fed to the photoconductive drum; a DC voltage application portion outputting, as an output, a DC voltage applied to the developing roller, and receiving a feedback voltage to adjust the output or stop the outputting; an AC voltage application portion connected to the DC voltage application portion, and applying to the developing roller, a voltage having the DC voltage outputted from the DC voltage application portion and an AC voltage superimposed on each other; a detection portion detecting occurrence of electric discharge between the developing roller and the photoconductive drum based on a variation in the DC voltage applied to the developing roller; a first resistor portion generating from the DC voltage applied to the developing roller the feedback voltage that is fed to the DC voltage application portion; a second resistor portion connected between the DC voltage application portion and the AC voltage application portion, and having a switching portion with which conducting on and off are switchable; and a control portion controlling the apparatus, recognizing whether or not electric discharge has occurred based on an output of the detection portion, and controlling the switching portion, at a time of printing, to bring the second resistor portion into a conducting state, and at a time of electric discharge detection in which while the AC voltage application portion is made to vary stepwise a peak-to-peak voltage of the AC voltage applied to the developing roller, a peak-to-peak voltage at which electric discharge start between the photoconductive drum and the developing roller is detected, to bring the second resistor portion into a non-conducting state.