DEVELOPING DEVICE

PROBLEM TO BE SOLVED: To provide a developer carrier capable of preventing SB from becoming too small and suppressing unstable conditions caused by the clogging of foreign matters or coating of a developer without needlessly reducing the carrying force of a developing sleeve.SOLUTION: The developing sleeve has a plurality of grooves extending in the longitudinal direction on the surface, and when the developer carrying amount on the developer sleeve after passing a regulation blade is defined as M/S(mg/mm), the gap between the tip of the regulation blade and the developing sleeve is defined as SB (mm) and the specific gravity of a two-component developer is defined as G (mg/mm), the gap SB between the tip of the regulation blade and the developing sleeve is 0.2 mm or more, 0.029≤M/S(mg/mm)/G(mg/mm)≤0.14, and the ratio α (groove ratio) occupying the grooves on the developer sleeve surface is set to satisfy the following relational expression: M/S(mg/mm)×1/4≤α×{SB(mm)+D(mm)}×G(mg/mm)