A developer accommodating unit includes: a flexible container including an opening for permitting discharge of a developer; a sealing member for forming a bonding portion between itself and the flexible container; an unsealing member; and an accommodating container. The bonding portion includes a first bonding portion extending in a longitudinal direction of the sealing member at a periphery of the opening in an upstream side of a peeling direction of the sealing member, a second bonding portion extending in the longitudinal direction at the periphery of the opening in a downstream side of the peeling direction, and a third bonding portion bonded upstream of the first bonding portion with respect to the peeling direction. When the sealing member exposes the opening, the bonding portion is peeled in the order of the third bonding portion, the first bonding portion and the second bonding portion.