An image forming system comprising: an image forming apparatus configured to form an image using toner; and a replenishment cartridge configured to supply toner to the image forming apparatus, wherein the replenishment cartridge includes a storing unit storing toner, a memory device including a storage element storing information, an insertion portion including a discharge opening for discharging toner from the storing unit, and a first rotary member rotatable for opening and closing the discharge opening, and wherein the image forming apparatus includes an installation portion to which the replenishment cartridge is attached with the insertion portion being a leading end side, a first electric contact portion that is provided inside the installation portion and configured to contact a second electric contact portion of the memory device included in the replenishment cartridge, in a state where the replenishment cartridge is attached to the installation portion, a regulation unit that includes a movable member rotatable to a first position and a second position, and is configured to regulate the replenishment cartridge by the movable member moving from the first position to the second position, and a control unit, characterized in that the regulation unit is configured to cause a state in which the replenishment cartridge cannot be detached from the installation portion, by rotation of the movable member from the first position to the second position, and the control unit starts communication with the memory device via the first electric contact portion and the second electric contact portion after the replenishment cartridge is regulated in the installation portion by the regulation unit. an image forming apparatus configured to form an image using toner; and a replenishment cartridge configured to supply toner to the image forming apparatus, wherein the replenishment cartridge includes a storing unit storing toner, a memory device including a storage element storing information, an insertion portion including a discharge opening for discharging toner from the storing unit, and a first rotary member rotatable for opening and closing the discharge opening, and a storing unit storing toner, a memory device including a storage element storing information, an insertion portion including a discharge opening for discharging toner from the storing unit, and a first rotary member rotatable for opening and closing the discharge opening, and wherein the image forming apparatus includes an installation portion to which the replenishment cartridge is attached with the insertion portion being a leading end side, a first electric contact portion that is provided inside the installation portion and configured to contact a second electric contact portion of the memory device included in the replenishment cartridge, in a state where the replenishment cartridge is attached to the installation portion, a regulation unit that includes a movable member rotatable to a first position and a second position, and is configured to regulate the replenishment cartridge by the movable member moving from the first position to the second position, and a control unit, an installation portion to which the replenishment cartridge is attached with the insertion portion being a leading end side, a first electric contact portion that is provided inside the installation portion and configured to contact a second electric contact portion of the memory device included in the replenishment cartridge, in a state where the replenishment cartridge is attached to the installation portion, a regulation unit that includes a movable member rotatable to a first position and a second position, and is configured to regulate the replenishment cartridge by the movable member moving from the first position to the second position, and a control unit, characterized in that the regulation unit is configured to cause a state in which the replenishment cartridge cannot be detached from the installation portion, by rotation of the movable member from the first position to the second position, and the control unit starts communication with the memory device via the first electric contact portion and the second electric contact portion after the replenishment cartridge is regulated in the installation portion by the regulation unit.