An image forming apparatus having an image carrier, a charging unit for charging
the image carrier and residual toner on the image carrier, a charging bias applying
unit, an electrostatic image forming unit, a developing unit for collecting the
residual toner on the image carrier and visualizing the electrostatic image, and
a developing bias regulating unit. The apparatus further comprises an image ratio
calculating unit for calculating an image ratio on the basis of the electrostatic
image, and a regulating unit for regulating a contrast potential between the developing
unit collecting the residual toner and the image carrier on the basis of a calculated
image ratio. In the apparatus, an occurrence of the problem of adhesion of toner
to a non-image area is prevented by fully collecting transfer residual toner also
in forming an image having a high image ratio.