Developing device with elastic film to block air input

A developing device comprising:

• a housing to contain a developer, the housing comprising an opening and a developer outlet to discharge a surplus of the developer;
• a developing sleeve provided in the housing and comprising a development region partially exposed to an outside of the housing through the opening;
• a magnetic member located inside the developing sleeve to generate a magnetic force and comprising a developing pole located to correspond to the opening and a conveying pole located at a downstream side of the opening in a rotation direction of the developing sleeve, the conveying pole having an opposite magnetic polarity to that of the developing pole;
• an elastic member comprising a fixed portion fixed to the housing at a position adjacent to a downstream edge of the opening, and an extension portion elastically in contact with the developing sleeve upstream of the conveying pole in the rotation direction of the developing sleeve, wherein the extension portion extends from the fixed portion and is bent from the fixed portion in a forward direction with respect to the rotation direction of the developing sleeve to be elastically in contact with an outer circumferential surface of the developing sleeve;
• and
• a regulating member located at an upstream side of the opening in the rotation direction of the developing sleeve to regulate a thickness of the developer supplied to the opening, wherein the regulating member is spaced apart from the outer circumferential surface of the developing sleeve by a regulation gap,
• wherein the regulation gap is equal to or greater than a minimum gap between the housing and the developing sleeve at the downstream side of the opening.