PURPOSE: To improve picture quality by the stable triboelectricity of toner by supplying a two-component developer which is charged electrostatically to the opposite polarity to a triboelectric separation electric field curtain, and supplying toner to a development area while separating its two components.

CONSTITUTION: When a mixture 10 is supplied from a hopper 12 onto a triboelectric separation type electric field curtain 1, the triboelectric donor 5 itself in the mixture is charged electrostatically to the plug polarity, so it is conveyed in a direction β and toner 4 with the minus polarity is conveyed in a direction α. Toner particles 4 conveyed in the direction α reach the development area sandwiched between a latent image carrier 11 and the electric field curtain facing it and attracted there to an electrostatic latent image (minus polarity) 13 with an alternating electric field based upon a driving voltage, so that development is carried out. Here, the toner 4 has stable triboelectricity by contact electrostatic charging with the triboelectricity donor 5, so the adverse influence of unstable triboelectricity upon an image becomes nil.