A method of sterilizing a bottle, comprising: sterilizing bacteria adhering to a preform made of resin by gasifying a sterilizer, discharging a sterilized gas toward a preform, now traveling, so as to adhere to the preform by discharging the sterilizer from a nozzle; activating the sterilizer adhering to the preform by blasting hot air to the preform; sterilizing the bacteria adhering to the preform and removing the sterilizer adhering to the preform; heating the preform to a temperature suitable for blow-molding treatment; and blow-molding the preform within a mold to mold the preform into a bottle, wherein the above-mentioned steps are performed subsequently in order, wherein after the bottle is molded in the mold, the mold is opened while being traveled, and the product bottle is then taken out of the mold, the bottle after taken out of the mold is conveyed till the hydrogen peroxide supply process starts while blasting an aseptic air from a mouth portion side, and by the blasting of the aseptic air, the bottle is conveyed directly below a hydrogen peroxide supply nozzle so as not to be contaminated by bacteria and the like fungus, wherein a cover is disposed in form of a tunnel so as to surround a traveling path of the bottle at a portion at which the bottle is conveyed toward the hydrogen peroxide supply nozzle, wherein the method is characterized in that a top portion of the tunnel-shaped cover covering the mouth portion of the bottle from an upper side thereof is formed as a roof having an inclining surface, to such top portion, nozzles through which the aseptic air is blasted toward the mouth portion of the bottle or traveling path are provided in form of line or slit, and according to such structure, the bottle travels with the aseptic condition being maintained, and the bottle blasted with the aseptic air is then sterilized by applying the hydrogen peroxide. activating the sterilizer adhering to the preform by blasting hot air to the preform; sterilizing the bacteria adhering to the preform and removing the sterilizer adhering to the preform; heating the preform to a temperature suitable for blow-molding treatment; and blow-molding the preform within a mold to mold the preform into a bottle, wherein after the bottle is molded in the mold, the mold is opened while being traveled, and the product bottle is then taken out of the mold, the bottle after taken out of the mold is conveyed till the hydrogen peroxide supply process starts while blasting an aseptic air from a mouth portion side, and by the blasting of the aseptic air, the bottle is conveyed directly below a hydrogen peroxide supply nozzle so as not to be contaminated by bacteria and the like fungus, wherein a cover is disposed in form of a tunnel so as to surround a traveling path of the bottle at a portion at which the bottle is conveyed toward the hydrogen peroxide supply nozzle, wherein the method is characterized in that a top portion of the tunnel-shaped cover covering the mouth portion of the bottle from an upper side thereof is formed as a roof having an inclining surface, to such top portion, nozzles through which the aseptic air is blasted toward the mouth portion of the bottle or traveling path are provided in form of line or slit, and according to such structure, the bottle travels with the aseptic condition being maintained, and the bottle blasted with the aseptic air is then sterilized by applying the hydrogen peroxide.