To prevent a flap (Pb) of an envelope (P) to stick to an envelope main body (Pa), provided is an image forming apparatus including: an image forming portion forming a toner image on the envelope; a fixing device fixing the toner image onto the envelope by heating the envelope while conveying the envelope on which the toner image is formed by the image forming portion; and a conveying roller pair (235) that rotates while nipping the envelope, onto which the toner image is fixed by the fixing device, to convey the envelope. A driven roller (233) of the conveying roller pair includes driven runners (331, 332) divided in a rotary shaft center direction, and one driven runner (332) located at one end is inclined in a direction separating from another driven runner (331) so that an outer peripheral surface (332a) of the one driven runner is brought into contact with a corner portion (22b) of a rubber roller (262).