An image forming apparatus includes a first image forming unit for forming a first image on a first image carrier, a second image forming unit for forming a second image on a second image carrier, a conveyor belt confronting the first and second image carriers for conveying an image receiving medium to the first and second image carriers successively. The apparatus further includes a first transfer roller for transferring the first image from the first image carrier to the image receiving medium, the first transfer roller being located at a first distance from a first transfer position of the first image carrier along a conveying direction of the image receiving medium, and a second transfer roller for transferring the second image from the second image carrier to the image receiving medium, the second transfer roller being located at a second distance from a second transfer position of the second image carrier shorter than the first distance along the conveying direction of the image receiving medium. A common transfer bias voltage is applied to the first and second transfer rollers to form first and second electric fields at the first and second transfer positions, respectively.