Developing unit using elastic supply roller

A developing unit, comprising:

• a case for accommodating toner;
• a developing roller rotatably supported by said case through a shaft;
• and
• a supply roller rotatably supported by said case through a shaft and formed by an elastic member arranged to be pressed against said developing roller in such a manner as to supply toner to the surface of said developing roller, wherein
• said elastic member forming said supply roller is comprised of an expanded material having a ratio of open cells of 30% or higher (expressed as a percentage),
• a depth of engagement of said supply roller to said developing roller is 0.4 mm or smaller, and
• the toner having a shape factor SF-1 of 150 or smaller, and a shape factor SF-2 of 140 or smaller.