There are provided a rotatable developer accommodating portion accommodating a developer, a discharge end portion provided at a bottom side with a discharge opening for discharging the developer accommodated in the developer accommodating portion, an engaging portion 30 engageable with a portion-to-be-engaged 11b with a mounting operation of the developer supply container 1 to displace the portion-to-be-engaged 11b in an upward direction U to bring the receiving opening into fluid communication with the discharge opening, and a swing shaft 41 rotatably supporting engaging portion 30 provided at such a position that opposite end portions of the engaging portion 30 a rotatable.