Abstract: Provided is an innovative method for sterilization or inactivation treatment of heat-resistant spore-forming bacteria that demonstrates a sufficient sterilization effect in a reliable manner and that can be implemented using simple equipment by reducing the heat resistance of heat-resistant spore-forming bacteria by the effect of decompression treatment in a high-pressure process, and by carrying out a heat sterilization treatment after a predetermined resting time has elapsed after the decompression to thereby sterilize and inactivate heat-resistant bacteria that have reduced heat resistance. A method for sterilizing or inactivating heat-resistant spore-forming bacteria by performing, as a pretreatment of a heat sterilization treatment, a high-pressure treatment in which a hydrostatic pressure of 50 MPa or more and 200 MPa or less is applied to an object under a temperature of 50° C.