A developing device includes a developer sleeve, a regulating portion including an edge portion at a closest position to a surface of the sleeve or a flat portion tilted, at the closest position, by an angle of 2 degrees or less relative to a contact flat plane contacting the surface of the sleeve, and a rectifying portion connected with the edge or flat portion. The rectifying portion has a concavely curved surface such that a rate of a decrease in a gap between the rectifying portion and the contact flat plane increases toward a downstream side of the developer feeding direction and is formed by smoothly connecting rectilinear or curved lines each of 0.2 mm or less except for the edge portion so that the gap between the rectifying portion and the contact flat plane monotonically decreases toward the downstream side of the developer feeding direction.