PROBLEM TO BE SOLVED: To disinfect a preform simply and rapidly.SOLUTION: At least inner surface in the entire surface including a mouth part (1a) of a preform (1) is preheated by spray of an aseptic hot air (H), then super heated steam (S) made by hydrogen peroxide mixed water of a 0.5-15% concentration of 150-500°C having higher pressure than air pressure is sprayed to at least the inner surface.