A developer supply container detachably mountable to an image forming apparatus, includes a container body, having a non-circular cross-section, for containing a developer, the container body having an arcuate portion and an extension upwardly extending from the arcuate portion; a discharge opening, formed in the arcuate portion for discharging the developer from the container body; a stirring member for stirring the developer in the container body, the stirring member having a rotation shaft provided in the arcuate portion and a flexible resin material sheet mounted on the rotation shaft; wherein the flexible resin material sheet includes a feeding blade for feeding the developer toward the discharge opening, the feeding blade being slidable relative to an inner surface of the arcuate portion and being non-slidable relative to a ceiling portion of an inner surface of the extension, and includes a stirring blade for stirring the developer, the stirring being slidable relative to a ceiling portion of the inner surface of the extension.