An erasable toner is prepared by mixing colored particles containing at least a color former compound, a color developer agent and a binder resin with de-coloring particles having a melting point higher than the fixing temperature of the colored particles. By using this toner, a colored image is formed by electrostatically transferring a toner image onto a medium, and heating the toner image at a temperature lower than the melting point of the de-coloring particles to form a fixed toner image in a color developed state, and the color of the fixed image is erased by heating the image to a temperature not lower than the melting point of the de-coloring particles. In this toner, the color developing function and the color erasing function are assigned to different particles so that the functions are separated from each other, and therefore, the formation of an image in a color developed state and the erasure thereof can be reliably and promptly achieved.