An image forming unit includes a first developer supply member that is arranged inside a developer container and supplies a developer to a developer carrier, a seal member of which a fixed end is fixed on a case.The case has a first wall part that extends from the fixed end obliquely downward with respect to a vertical direction and a second wall part that continues from the first wall part and extends along an outer peripheral surface of the first developer supply member, and a first distance between an inner peripheral surface of the first wall part and the outer peripheral surface of the first developer supply member becomes smaller with increasing distance from the fixed end of the seal member.