PURPOSE: To decrease the energy quantity required for fixing and to assure durability by using a resin contg. a specific diolefin high-molecular polymer as a sub-range as a binder and incorporating any of Cu, Ni, Ti, Al, Co, Mn, Zn, Fe alone or the metal compd. thereof into the toner.

CONSTITUTION: The resin contg. 3 to 80wt.% diolefin high-molecular polymer having ≥50°C glass transition point as the sub-range is used as the binder and any of the Cu, Ni, Ti, Al, Co, Mn, Zn, Fe alone or the metal compd. thereof is incorporated therein. The energy quantity necessary for fixing is, therefore, decreased while the durability of the toner is maintained. This toner is widely effective as the toner for establishing the process of a low running cost with image forming devices, i.e., printers, copying machines or facsimiles in this way. An extremely high effect is expected particularly in the reduction of the running cost, the improvement of the image density, etc., when the toner is applied to the insulating toner of a heat fixing system.