An image forming method, including the steps of: charging each surface of a plurality of amorphous-silicon-based photoreceptors; exposing the each surface of the amorphous-silicon-based photoreceptors to form respective color latent images of yellow, magenta, cyan and black; developing the respective color latent images with corresponding color toners to form respective color visible toner images; and transferring the respective color toner images successively to be piled up on a toner image receiving member, wherein the color toner of each color contains grains having volume average grain size (D4) of 3-7 .mu.m and number average primary grain size of 40-800 nm, and the relationship of 1.04.ltoreq.B/A.ltoreq.1.4 (6.ltoreq.A.ltoreq.30) is satisfied between an exposure size (A .mu.m) in the main scanning direction in the exposing step and a development size (B .mu.m) corresponding to the exposure size (A .mu.m) in the developing step.