PURPOSE: To safely and perfectly sterilize the subject food without damaging the container by setting a food or raw material-charged solid container such as synthetic resin container in the inner cavity of a mold and subsequently heating and cooling the container, etc., under specific conditions.

CONSTITUTION: A solid container 1 made of a synthetic resin, etc., and charged with a food or raw materials thereof is set in a mold 5 having an inner cavity 6 capable of receiving the container in a tightly contacting state, and a press plate 8 is loaded on the upper surface of the mold. The thermally fusing sections of the container and the press plate are tightly pressed to enable the conduction of heat to contents in the container without being affected pressures in the container and outside the container. The container, etc., are heated in a heating container 12 to a sterilization temperature of 120°C to a temperature just below the heat resistant temperature of the resin, held at the high temperature for a short time and immediately forcibly cooled to the ordinary temperature within a short time, thereby rapidly heating and subsequently cooling the preserving food packed in a solid container.