PURPOSE:To stably maintain ideal density by supplementing toner corresponding to toner consumption, measuring toner density, and setting the shape below a nap cutting plate so that specific density is obtained. CONSTITUTION:Th toner is a toner storage part 12 is agitated and circulated by auger screws 13 and 14. The output of a toner sensor 15 is inputted to a control part 30, which puts a toner hopper 18 in operation when the input value exceeds a reference value to supplement a specific amount of toner into the toner storage part 12. When the toner density is higher than the specific toner density, the pedestal 16 of the nap cutting plate 17 is moved toward a developing roll 11 and thus adjusted to set the pressure below the nap cutting plate 17 high. Consequently, the toner density can be maintained with high accuracy even under toner replenishment control based upon the detection output of the toner sensor depending upon the magnetic permeability.
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