DEVELOPING DEVICE

PROBLEM TO BE SOLVED: To ensure the strength of a developing casing by making a developer discharge port in an appropriate position in a two story developing device. SOLUTION: The inside of a developing casing 73 of the two-story developing device is divided with a partition plate 74 into a developing chamber 75 in a low position and a developer stirring chamber 76 in a high position, which has carrying rolls 78 and 79 therein. The developing device circulates developer. In the developing device, rotary spiral vanes are used as carrying rolls 78 and 79. The vanes are excellent in the ability to carry developer in the direction of thrust. A developer discharge port 82 of the smallest size is made near a downstream area in a developer circulation path in the second stirring chamber 76. The developer is discharged highly efficiently while ensuring the strength and sealing properties of the developing casing.