| 摘要 |
A developing device of an electrophotographic image forming apparatus has a first roller and a second roller disposed in a peripheral contact with the first roller to define a contact region therebetween so that the first roller is capable of supplying and collecting a toner to and from the second roller in the contact region. The first roller has a core and a polyurethane foam layer. The polyurethane foam has an open ratio of cells of 2% or more and 50% or less and a hardness of 1 gf/mm or more and 6 gf/mm or less, the hardness being defined by a load per unit length in a longitudinal direction of the first roller, the load being determined by forcing the peripheral surface of the polyurethane foam layer against a substrate, measuring a load necessary for the polyurethane foam layer to be compressed by 30% in thickness, and dividing the load by a length of the polyurethane foam layer in the longitudinal direction. The first and second rollers are disposed so that the contact region has a peripheral width of 3 mm or more and 8 mm or less.
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