Patent ID: 7979011

Claim:
An image forming apparatus comprising: a photoconductive drum that carries a toner image on a circumferential surface thereof; a developing roller that is arranged opposite the photoconductive drum with a gap in between, and that carries toner when engaging in an image forming operation; a detecting portion that detects an occurrence of electrical discharge between the photoconductive drum and the developing roller; a control portion that controls the apparatus, that receives an output of the detecting portion, and that recognizes, based on the output, the occurrence of the electrical discharge; a direct voltage applying portion that is connected to the developing roller so as to supply toner to the photoconductive drum; and an alternating voltage applying portion that is connected to the developing roller so as to supply the toner to the photoconductive drum, and that, when an electrical discharge detecting operation is performed in which the occurrence of the electrical discharge is detected by use of the detecting portion with an alternating voltage applied to the developing roller changed step by step in accordance with an instruction from the control portion, applies, to the developing roller, the alternating voltage having a duty ratio and a frequency different from the alternating voltage applied for the image forming operation, so that the electrical discharge is made to occur simply in a direction in which an increase in current induced by the electrical discharge is smaller for an increase in potential difference, grasped in advance, between the photoconductive drum and the developing roller.