Patent ID: 8874008

Claim:
A developing device supplying a two-component developer to a developing roller, while causing the developer to circulate in a circulating passage including a first conveying passage and a second conveying passage arranged in parallel to each other, and while ejecting a part of the developer to outside via an ejection passage formed as an extension of the first conveying passage on a downstream side in a developer conveying direction, the developing roller being provided along the first conveying passage, the developing device comprising: a first communication path provided as a branch of the first conveying passage on the downstream side in the developer conveying direction and configured to allow the first conveying passage to communicate with the second conveying passage; a first conveying part configured to convey the developer in the first conveying passage toward the first communication path; an entrance allowance unit configured to allow the developer to enter the ejection passage from the first conveying passage depending on a pressure of the developer in the first conveying passage, the first conveying part including a main conveying part and a sub-conveying part, the main conveying part being provided in a region corresponding to the developing roller, and the sub-conveying part, provided downstream of the main conveying part in the developer conveying direction, conveying a smaller amount of developer per unit time than the main conveying part; and a second communication path provided at a position corresponding to an end of the main conveying part and upstream of the sub-conveying part in the developer conveying direction, and allows the first conveying passage to communicate with the second conveying passage; wherein: the second communication path, the first communication path, and the ejection passage are arranged in order along the developer conveying direction in the first conveying passage; the first conveying passage and the second conveying passage are arranged in parallel to each other with a partition wall therebetween, the first communication path and the second communication path are a first opening and a second opening provided in the partition wall, respectively, and a lowest portion of the second opening is higher than a lowest portion of the first opening in position in a vertical direction.