Image forming apparatus and method of controlling the same

An image forming apparatus comprising:

• a photoconductor;
• a charging member provided in proximity to the photoconductor;
• a first power supply circuit configured to supply alternating-current power to the charging member;
• a detector configured to detect a current value of an alternating current which flows to the charging member;
• and
• a controller configured to control an operation of the first power supply circuit,
• the controller being configured to lower a frequency of alternating-current power supplied to the charging member by the first power supply circuit when the current value detected by the detector in application of a voltage of a prescribed value to the charging member by the first power supply circuit is equal to or smaller than a predetermined value.