PURPOSE:To obtain the titled one-component type toner high and always stable in fluidity and offset causing temp., and capable of forming a good visible image by incorporating a specified modified polyolefin wax and heat treating it in a suspension state. CONSTITUTION:A modified polyolefin wax used here has a softening point of 80-180 deg.C and it is obtained by block or graft copolymerizing (b) aromatic vinyl monomer, such as styrene or 1-phenylpropene, with (a) polyolefin, such as ethylene, propylene, or butene-1 (co)polymer, in an amt. of 0.1-15wt% monomer based on the copolymer. (A) a binder resin made of a vinyl resin, (B) a magnetic powder having 5-30mum average particle diameter, and (C) said wax in an amt. of 1-20wt% of the total wt. of toner are thermally kneaded, cooled, pulverized, and classified, and then, heat treated in a gaseous stream heated to 100-350 deg.C for about 0.01-0.1sec.