A preform (31) is sterilized by a preform sterilizer (11). The preform (31) is blow-molded by a blow-molding device (13) to manufacture a container (30). Next, the container (30) is filled with a culture medium by a filling device (20) without sterilizing the container (30) by a container sterilizer (15), and the container (30) is plugged by a plugging device (21). Thereafter, it is verified how much microorganism survive or propagate in the culture medium in the container (30). A degree of sterilization in the container sterilizer (15) is adjusted on the basis of a verification result.
