An image forming apparatus includes a transfer bias set up section and a developing bias set up section. The transfer bias set up section sets a transfer bias applied to each transfer member so that the transfer bias applied to a transfer member corresponding to a photosensitive member on the most downstream side is greater than a transfer bias applied to a transfer member other than this transfer member. The developing bias set up section sets a developing bias applied to each developing member to a first developing bias in a single-side printing mode, and sets up the developing bias applied to each developing member in formation of an image on a first surface and in formation of another image on a second surface to a second developing bias lower than the first developing bias when the image formed on the second surface is a color image.