Patent ID: 7885563

Claim:
A development apparatus for developing an electrostatic latent image formed on an electrostatic latent image carrier, comprising: a developer carrier for carrying and affixing developer charged to a predetermined electric potential to said electrostatic latent image carrier by rotating in a direction facing a circumferential surface of said electrostatic latent image carrier and for applying a development bias voltage V D that is a prescribed DC voltage, a first power source apparatus applying, to the developer carrier, the voltage V D ; a developer supply unit with a circumferential surface formed of a prescribed elastic material with a hardness of H AF set to 20≦H AF ≦80 measured by an Asker F-type and disposed rotatably contacting said developer carrier to supply developer to said developer carrier so that an amount of push δ, defined as the amount pushed by the contact between said developer supply unit and said developer carrier, is 0.5 mm or below; a second power source apparatus applying, to said developer supply unit, a developer supply bias voltage V S periodically alternating between voltages V SH and V SL , each having the same polarity as a charge polarity of the developer, said second power source apparatus outputting periodically at a frequency f of 500 HZ≦f≦5000 HZ a second peak value at said voltage V SH and having a same polarity as a polarity of the charge of said developer, after outputting a first peak value at said voltage V SL and having the same polarity as the polarity of the charge of said developer; and a developer layer formation unit for thinning developer supplied to the circumferential surface of said developer carrier by said developer supply unit, wherein said developer supply bias voltage V S superimposing AC voltage on the prescribed DC voltage is applied to said developer supply unit, and has said frequency f of 500 HZ≦f≦5000 HZ and the condition 1≦|V SH −V D |/|V D −V SL |≦5 is fulfilled with V SH as a large peak value with a polarity opposite to the charge polarity of the developer and V SL as the large peak value with the same polarity as the charge polarity of the developer.