The development device of this invention includes a developer bearing member, a magnet, and a developer regulation member. The magnet is fixedly disposed within the interior of the developer bearing member. The developer regulation member includes at least a magnetic member. And the thickness of this magnetic member along the rotational direction of the developer bearing member is between 0.2 mm and 0.4 mm inclusive. Moreover, if the distance over the developer bearing member, from the position thereupon which the center of the magnetic member along the rotational direction opposes, to the position thereupon at which the magnetism of that magnetic pole which is disposed closest to that position is a maximum, is termed L (mm), and the diameter of the developer bearing member is termed D (mm), then the magnetic member is disposed within the range in which the relationship 0≦L/D≦0.044 holds.