An image forming apparatus includes: a photoconductive drum; a developing roller carrying toner; a DC voltage application portion outputting a DC voltage to be applied to the developing roller, and receiving a feedback voltage; an AC voltage application portion applying an AC voltage to be applied to the developing roller; a detection portion detecting occurrence of electric discharge; a first resistor portion generating a 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 switching portion, at the time of printing, to bring the second resistor portion into a conducting state and, at the time of electric discharge detection, to bring the second resistor portion into a non-conducting state.