PURPOSE: To obtain the developer formed by a conductive fine particle toner having excellent fine line reproducibility, gradation characteristic, etc., for developing electrostatic latent images by mixing a specific toner and specific magnetic particles, thereby constituting the developer.

CONSTITUTION: This developer is obtd. by mixing the toner having 0.5 to 5μm average grain size based on weight (average grain size) and about ≤ 1×1010Ωcm specific volume resistivity. The toner is obtd. by adding coloring agents, conduc tive particles, and other necessary fine particles, etc., to a binder resin, dissolv ing and kneading the mixture to disperse these components into the binder resin and adjusting the mixture to a desired grain size distribution by grinding and classifying after cooling. The magnetic particles may be the particles of magnetic materials, such as various kinds of magnetites, ferrites and hematites, themselves or may be the particles formed by dissolving and kneading the fine particles of these magnetic particles in and with a thermoplastic resin and grinding the mixture. Printed matter having high fineness and high grada tion characteristic is obtd. in this way.