An image forming apparatus includes an apparatus main body, a photoreceptor drum, a charging apparatus, a developing device, a transfer apparatus, a charging bias applying unit, a developing bias applying unit, a bias adjusting unit, and a print density measurement unit. The bias adjusting unit controls the charging bias applying unit to form a plurality of electric potential areas of electric potentials with different magnitudes. The bias adjusting unit applies a predetermined developing bias corresponding to a target electric potential to the developing roller, so as to form a plurality of toner images by electric potential differences between the developing bias and the plurality of electric potential areas. The bias adjusting unit decides a value of a charging bias corresponding to the target electric potential from measurement results of print densities of the plurality of toner images measured by the print density measurement unit.