A sterilization method that generates a sterilization gas by vaporizing a sterilizing agent supplied to a chamber having reduced pressure, and sterilizes an object to be sterilized using the sterilization gas, said method comprising (a) a first step for reducing the pressure of the chamber to a prescribed pressure, and (b) a second step for generating the sterilization gas by injecting the sterilizing agent into the chamber after the first step. The second step comprises (b1) a first sub-step for generating the sterilization gas by injecting a prescribed amount of the sterilizing agent into the chamber, (b2) a second sub-step for standing by after the first sub-step until a predetermined criterion is satisfied, and (b3) a third sub-step for repeating the first sub-step and the second sub-step a prescribed number of times.
