An image forming method of forming a full-color image in which black can be expressed in addition to a color expressed by diffracted light. Each of plural diffraction gratings R, G, and B is transferred onto a base material from a transfer sheet in which the plural diffraction gratings R, G, and B are laminated, and the plural diffraction gratings R, G, and B are different from one another in a color of diffracted light observed in a particular direction. A black ink layer constituted by black ink is formed on the base material. Thereby, a color image is formed on the base material, in which a color to be expressed of each pixel is expressed by a combination of luminances of colors corresponding to the diffraction gratings R, G, and B and the black ink.