Image forming apparatus with toner supplying roller

A developing device has a developer bearing member, a housing adapted to accommodate a developer, and a supply roller adapted to supply the developer within the housing for the developer bearing member. The supply roller has an outer circumferencial foam layer made of resin or rubber. The foam layer has an air permeability of 150-200 ml/cm /s, a hardness of 50-200 N, and an average cell density of 20-40 per 25 mm width.