PURPOSE: To stably obtain an excellent image without having the image defect of a void, missing, etc., even in a normal operation and an operation after a developing device is left to stand for a long period on the developing device which externally fits a developing sleeve having an inside diameter a little longer than the outside diameter of the driving roller to a driving roller, pressing both end parts of the developing sleeve on the driving roller from one side, by a pressing member, and allowing a loosened part on the opposite side, to be brought into contact with an electrostatic latent image carrier.
CONSTITUTION: In the developing device 10 externally fitting the developing sleeve 13 to the driving roller 15, pressing the sleeve on the roller 15 by a pressing/guiding member 21, and allowing the loosened part 130 on the opposite side to bring it into contact with a photosensitive drum PC, the sleeve 13 is made of a material having the Young's modulus of E ≤500(kg/mm2), and a constitution is adopted so that an angle α between a line connecting a sleeve guiding end part (a) by the guiding member 21 with the center 0 of the roller 15, and a line connecting the center 0 of the driving roller 15 with the center PCO of the drum PC, and a difference L the outside diameter between the roller 15 and the sleeve 13, satisfy the relation of [(117/α)-0.7].
MIZUNO HIROSHI
FUJIWARA TOSHIMITSU
