A method for manufacturing contents such as a drink contained in a container such as a PET bottle by filling the contents in the container, sealing the container and sterilizing the container includes steps of: filling the contents in a polyester container having a non-crystallized neck portion; sealing the container; and sterilizing the container in such a manner that temperature of the neck portion of the container during sterilization is maintained within a temperature range which is 61° C. or over and less than a glass transition temperature determined by moisture content of the container.