An image forming apparatus includes an image bearing member and a charge member contacted to the image bearing member for electrically charging the image bearing member. An oscillating voltage including an AC voltage component is applied to the charge member. A first detector detects an AC current applied to the charge member and a second detector detects the AC current corresponding to a peak or a neighborhood of the peak of the AC voltage. A controller effects control such that current detected by the second detector is a predetermined level when the current detected by the first detector is within a predetermined range, and such that current detected by the first detector is a predetermined level when the current detected by the first detector is outside the predetermined range.