A developer supply container detachably mountable to an image forming apparatus, the developer supply container comprising a discharge opening for permitting discharging of a developer; a container body for accommodating the developer; a snap hook member having an engaging projection for snap-hook engagement with an engageable member of the image forming apparatus; a feeding portion for feeding the developer from the container toward the discharge opening by a rotating force received by the engaging projection from the engageable member; wherein snap hook member has a bending modulus of 1400 20000 MPa.