An image forming apparatus includes an image density control feature based on a result detected by an image density detection portion, where a developer amount per 10 mm in a longitudinal direction of a first chamber of a developer carrying member is Y (g), a developer carrying velocity in the longitudinal direction inside the first chamber is V.sub.D (mm/sec), a toner carrying amount per unit area on an image bearing member when forming a maximum density is M (mg/cm.sup.2), a surface movement velocity of the image bearing member is V.sub.p (mm/sec), and a distance from a position furthest downstream in a developer conveyance direction in a maximum area in which development is possible on the developer carrying member to a predetermined detection position in the maximum area in the longitudinal direction is X (mm), and the following relation is satisfied: X.ltoreq.(45.times.Y.times.V.sub.D)/(M.times.V.sub.p).