An oxidation process apparatus according to one embodiment of the present invention includes: a substrate holder provided in a processing chamber and having a substrate holding surface; a gas introduction unit for introducing an oxygen gas; a cylindrical member; and a substrate holder drive unit for changing relative positions of the substrate holder and the cylindrical member to allow the substrate holding surface and the cylindrical member to form an oxidation process space. The cylindrical member is provided so as to form a gap between the cylindrical member and the substrate holder during formation of the space. The oxygen gas is introduced restrictively into the space. The oxygen gas introduced from the gas introduction unit is evacuated through the gap.