PURPOSE: To provide a culture system for sterilely producing substances and a sterile validation technique, enabling sterilizing conditions to be established and sterilization effect to be quantitatively evaluated using heat-resistant ascospore bacteria resistant to high-pressure steam sterilization.

CONSTITUTION: A culture tank 1 is filled with heat-resistant ascospore bacteria and a culture fluid optimal for proliferating them through a nozzle 4 for filling indication bacteria followed by starting high-pressure steam sterilization process, and throughout the process, the fluid in the tank 1 is taken with time via a sampling nozzle 6. After completing the sterilization process, the ascospore bacteria is cultured for a specified time at a temperature optimal for proliferation thereof, and the fluid in the tank 1 is then taken via the sampling nozzle 6. The above operation is conducted several times at time intervals for several sterilization processes differing from one another.