A heat sensitive ink sheet has a heat sensitive ink layer which is formed of a heat sensitive ink material comprising colored pigment and thermoplastic resin such as amorphous organic polymer. An image receiving sheet having a support sheet and an image receiving layer thereon, the support sheet of the image receiving sheet being a porous sheet made of plastics which have fine pores therein. An image forming method is conducted by using the heat sensitive ink sheet and an image receiving sheet by area gradation by the use of a thermal head or laser beam.
