Patent ID: 8693903

Claim:
An image forming apparatus, comprising: a rotatable image bearing member; a first charging roller for electrically charging said image bearing member by contacting said image bearing member to generate electric discharge between said first charging roller and said image bearing member; a second charging roller for electrically charging said image bearing member, charged by said first charging roller, by contacting said image bearing member; a toner image forming portion, provided downstream of said second charging roller and upstream of said first charging roller with respect to a rotational direction of said image bearing member, for forming a toner image on said image bearing member charged by said second charging roller; a power source for applying, to said first and second charging rollers, a charging voltage in the form of a DC voltage biased with an AC voltage common to said first and second charging rollers; a detecting portion for detecting an AC current passing through said second charging roller; and a setting portion for setting, on the basis of the AC current detected by said detecting portion when an AC voltage is applied to said second charging roller, a value of a peak-to-peak voltage of the AC voltage of the charging voltage.