An agitator includes a film formed with one or more slits. The film may be partitioned into two or more areas by the slits, substantially equally in an axial direction of a rotating shaft of the film. In both ends of a film holding member, supporting plates may be disposed at positions facing outer ends of both end areas of the film with respect to the axial direction. With this structure, during rotation of the agitator, greater stress may be produced in the outer end of each end area than in an inner end of each end area and a center area in its entirety. Thus, a component applied in a direction along the rotating shaft may be applied to a direction in which developer is fed, so that an adequate amount of developer may be supplied.