An image forming apparatus for forming a toner image on a print medium with a developer composed of toner and carriers, wherein when the first distance is longer than the second distance, an average gap between the first peripheral surface and a member that faces to the first peripheral surface in an area with a length of the first distance extending upstream from the closest point with respect to the specified direction is smaller than an average gap between the first peripheral surface and a member that faces to the first peripheral surface in an area with a length of the first distance extending downstream from the closest point with respect to the specified direction.