Developing unit having a conveying fin for loading a supply roller with toner

A developing unit, comprising:

• a case for accommodating toner;
• a developing roller rotatably supported by said case through a shaft;
• 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;
• and
• a conveying fin rotatably supported by said case through a shaft in such a manner as to convey toner to the surface of said supply roller, wherein said developing roller, said supply roller and said conveying fin are sequentially disposed in a horizontal direction and are configured such that the number of revolutions per unit time of said conveying fin is not less than {fraction (1/50+L )} of number of revolutions per unit time of said supply roller nor more than {fraction (1/20+L )} of the same.