An image forming apparatus includes an image forming portion, an image input portion, a transfer unit, a transfer voltage power supply, and a control portion. The transfer unit includes a transfer roller having a metal shaft and an elastic layer laid around the outer circumferential face of the metal shaft to form a transfer nip by keeping the elastic layer in pressed contact with an image carrying member, and transfers a toner image formed on the image carrying member to a recording medium as it passes through the transfer nip. The transfer unit includes, as the transfer roller, a first roller, and a second roller having a larger axial-size elastic layer compared to the first roller. The control portion arranges first or second roller opposite the image carrying member according to width-direction sizes of the recording medium and the image data fed to the image input portion.