An image forming apparatus, which is capable of bringing an output density close to a target density even if a charge amount of toner particles changes, includes an image forming unit having an image carrier and a developing unit, a storage unit storing a saturation charge amount of toner particles, and a control unit. The control unit forms a patch image using the image forming unit, measures the density of the patch image to obtain a first potential that is a contrast potential corresponding to a target density, estimates the charge amount of the toner particles in the developing unit to obtain a first charge amount, obtains a second potential from the first potential, the first charge amount and the saturation charge amount, and sets the second potential as the contrast potential.