A developing device includes a sealing member for sealing an end of a developing roller to prevent developer from leaking from the interior of a casing. The casing includes a first plane and a second plane. A blade is mounted to the first plane and the blade regulates the amount of developer on the developing roller. The second plane is positioned upwardly of the first plane. The sealing member is positioned so that an end surface is located between the first plane and the second plane, and is mounted to the casing. The blade is mounted so as to press the end surface of the sealing member.