PURPOSE: To obtain a developer stable against repeated development by continuous use or against changes in temp. or humidity and showing high triboelectric characteristics, and to provide a developing device with which a uniform thin layer can be formed on a developer carrier body and an electrostatic latent image can be accurately visualized on a photosensitive drum or an image forming medium without causing development fog or scattering of the developer.

CONSTITUTION: The developer consists of a binder resin containing a coloring agent and a compd. classified as a color index Pigment Blue 27. The compd. classified as the color index Pigment Blue 27 is preferably incorporated by 0.1-10wt.% of the binder resin.