An image forming method comprising steps of: preparing a medium to be formed an image thereon, the image being based on signals of image data; forming the image directly on the medium in an ink jet system that discharges oil-based ink by utilizing electrostatic fields; rolling an adhesive roller on the medium before and/or during forming the image on the medium; adhering dust existing on the medium to the adhesive roller in order to remove the dust from the medium; and, fixing the image on the medium.