There are provided a developer accommodating portion for accommodating the developer, a discharge portion formed with a discharge opening for discharging the developer accommodated in the developer accommodating portion, and an engaging portion 30. The engaging portion 30 is engaged with an engaged portion 11b with a mounting operation of a developer supply container 1 to displace a developer receiving portion 11 in an upward direction U so that the receiving opening communicates with the discharge opening. The engaging portion 30 has a holding portion 31 which is provided rotatably about a rotation shaft 41 and is provided with holding portion 21 to be engaged with the engaged portion 11b to hold the engaged portion 11b. With the mounting operation, the engaging portion 30 rotates about the rotation shaft 41 so that the engaged portion 11b held by the holding portion 31 moves upward U.