An image forming operation for forming an image on one recording material includes a developing bias application unit applying a developing bias to a developer bearing member and a supply bias application unit applying a supply bias to a developer supply member. At the start of image formation, an absolute value of the developing bias is greater than an absolute value of the supply bias, and in a center or latter half of the image formation period, the developing bias and the supply bias have equal potential, and then the absolute value of the developing bias becomes smaller than the absolute value of the supply bias, until the end of image formation.