an ozone processing device includes : a mounting base on which a substrate is mounted ; a heating device to heat the substrate on the mounting base ; a plurality of plates facing the substrate on the mounting base and equipped with discharge openings on the surface facing the substrate that discharge ozone gas in the direction of the substrate ; and a gas supply device supplying ozone gas to the discharge openings of the plates to allow them to discharge gas . the plates are arranged in a co - planar manner with gaps formed between adjacent plates . the plates have a small volume so that even if there is heat transfer between the plates and the substrate , thermal equilibrium is achieved between the plates and the substrate in a short time , thus making temperature management of the substrate easy .