To attain high transfer efficiency of a toner image to an insertion part.

An intermediate transfer belt 28 has filler particles 82 uniformly doped everywhere inside or only on a top coating layer (in a multiple layer intermediate transfer belt). The average diameter of the particles 82 is smaller than that of toner particles which partly constitute the developer used in an image forming process. The toner particle 84 has a diameter of nearly 7 μm, and the diameter of the filler is 40 nm to 5 μm, the roughness provided by the filler has a wavelength in the range of 20 nm to 3 μm, and the distance from the peak to the valley is in the range of 20 nm to 5 μm. By giving such a relative dimension between the toner and the filler particle, a comparatively fixed area is maintained between the tone particles and the belt. Since the possibility of the toner sticking to the belt is reduced, and only a smaller transfer electrostatic field is required.