PROBLEM TO BE SOLVED: To provide a mechanism which can switch between a sterilization treatment using a concentrated sterilization agent and a sterilization treatment using a non-concentrated sterilization agent without changing a sterilization process.SOLUTION: In a concentration mode for executing a sterilization treatment using a concentrated sterilization agent, a sterilization agent supplied from a supply unit is concentrated in a concentration oven, and, after the inside pressure of a sterilization chamber is reduced to a specified pressure by a vacuum unit, the concentrated agent is delivered to a pipe connected to the sterilization chamber. In a non-concentration mode for executing a sterilization treatment using a non-concentrated sterilization agent, after the inside pressure of the sterilization chamber is reduced to a specified pressure, the sterilization agent is supplied from the supply unit to the concentration oven, and delivered to the pipe connected to the sterilization chamber.
