The objective is to provide a high-pressure treatment apparatus with which the pressure or temperature in a treatment chamber can be efficiently adjusted in a short period of time without an overall significant increase in the size or complication of the apparatus. The high-pressure treatment apparatus has a pressure-resistant container having pressure-resistant walls surrounding a treatment chamber, a lid member that closes an open end of the pressure-resistant container, a supply means that supplies a process fluid into the treatment chamber, a partition wall that is thinner than the pressure-resistant wall and is provided along the inside surface of said pressure-resistant container to form a partitioned chamber with said inside surface, and a heat transfer control means. Said heat transfer control means controls heat transfer between said treatment chamber and said partitioned chamber by heating or cooling a heating medium outside the container and feeding said heating medium into said partitioned chamber.