Cones whose rotation axes are substantially parallel to each other and whose sides maintain a constant interval therebetween are provided in a driving force transmission unit to transmit a driving force to a developer feeding member, a roller to transmit the driving force is provided between the cones, a position of the roller is moved in accordance with rotation of one cone or the other, and a rotational speed of the developer feeding member to which the driving force is transmitted from one cone changes with an increase in a number of revolutions of s driving force transmission unit.