An aseptic filling method comprising: a preform sterilization step where a preform is sterilized; a preform heating step where the sterilized preform is heated to a molding temperature; a molding step where the heated preform is molded into a container by a molding unit; a container sterilization step where the molded container is sterilized; a filling step where the sterilized container is filled with sterilized contents in an aseptic atmosphere; and a sealing step where the container filled with the contents is sealed by a sterilized lid member, the preform and the container being made to continuously travel, wherein assuming sterilizing ability in the preform sterilization step as X, the preform sterilization step being performed by performing any one, two or more selected from contact of a sterilizer with the preform, irradiation with electron beam to the preform, irradiation with light containing ultraviolet rays to the preform, contact of hot water with the preform, and contact of superheated steam with the preform and characterised in that assuming the sterilizing ability within a range from the preform heating step to the container sterilization step as Y, the container sterilization step being performed by performing any one, two or more selected from contact of a sterilizer with the container, irradiation with electron beam to the container, irradiation with light containing ultraviolet rays to the container, and contact of hot water with the container, a following formula is satisfied 5 ≤ X + Y ≤ 10 where Y ≥ 0; and wherein the molding unit is not sterilized, such that there is a possibility that the preform is contaminated with bacteria and the like during a period where the preform is conveyed through the molding unit. a preform sterilization step where a preform is sterilized; a preform heating step where the sterilized preform is heated to a molding temperature; a molding step where the heated preform is molded into a container by a molding unit; a container sterilization step where the molded container is sterilized; a filling step where the sterilized container is filled with sterilized contents in an aseptic atmosphere; and a sealing step where the container filled with the contents is sealed by a sterilized lid member, the preform and the container being made to continuously travel, wherein assuming sterilizing ability in the preform sterilization step as X, the preform sterilization step being performed by performing any one, two or more selected from contact of a sterilizer with the preform, irradiation with electron beam to the preform, irradiation with light containing ultraviolet rays to the preform, contact of hot water with the preform, and contact of superheated steam with the preform and characterised in that assuming the sterilizing ability within a range from the preform heating step to the container sterilization step as Y, the container sterilization step being performed by performing any one, two or more selected from contact of a sterilizer with the container, irradiation with electron beam to the container, irradiation with light containing ultraviolet rays to the container, and contact of hot water with the container, a following formula is satisfied 5 ≤ X + Y ≤ 10 where Y ≥ 0; and wherein the molding unit is not sterilized, such that there is a possibility that the preform is contaminated with bacteria and the like during a period where the preform is conveyed through the molding unit.