An image forming apparatus includes a latent image carrier, a charging device, a latent image forming device, a developing device, a transfer device, a toner amount detector, and a control circuit to execute an imaging condition determination process. The control circuit obtains a linear approximation formula of a developing potential and an amount of toner according to an exposure potential of the patch pattern and a detected amount of toner to calculate a developing gamma and a developing start voltage according to a gradient of the linear approximation formula, determines target charging potential, exposure potential and developing bias according to the developing gamma and the developing start voltage, determines an amount of a background potential to be corrected according to a difference between the developing start voltage and a target developing start voltage obtained according to environmental information, and corrects the target charging potential.