An engaging portion 30 is provided which is engageable with a portion-to-be-engaged 11b a displaceable integrally with a developer receiving portion 11 with a mounting operation of a developer supply container 1 to displace 11 in an upward direction U to bring a receiving opening into communication with a discharge opening. An engaging portion 30 includes a first engagement surface 31a extending in the upward direction U as going toward a developer accommodating portion of the developer supply container 1, and a second engagement surface 32a provided at a position closer to the developer accommodating portion than the first engagement surface 31a. When the receiving opening in communication with a shutter opening, a height of an end of the first engagement surface 31a close to the developer accommodating portion is higher than the second engagement surface 32a.