present invention all kinds of dyes and pigments heretofore known as such a coloring agent may be used for example carbon black nigrosine a metal complex of monoazo dye iron oxide black ultramarine graphite phthalocyanine blue chrome yellow benzidine yellow and quinaeridone series organic pigment hydrophobic silica fine particles may be adhered fast to the surface of the toner particles to obtain a toner which is further improved in the agglomeration and impact resistance however when the toner particles are merely mixed with the hydrophobic silica fine particles the resulting toner becomes undesirably deteriorated in its effect if a great many of copies are made with the toner therefore it is preferable to cause the silica fine particles to adhere fast to the surface of the toner particles for example in such a manner that the particles of the two are floated and suspended in gas to form a fluidized bed under states of which heating is conducted to the extent that the toner particles are softened what is meant by the 34 hydrophobic silica fine particle 34 is fine powder comprising silicon dioxide which has an average particle size of some 1 100 m u03bc and composition in which the hydrogen of the silanol group present in the.