A verification method of a content filling system which includes a preform sterilizer which sterilizes a preform, a blow-molding device which manufactures a container by blow-molding the preform sterilized by the preform sterilizer, a container sterilizer which sterilizes the container manufactured by the blow-molding device, a filling device which fills the container sterilized by the container sterilizer with a content, and a plugging device which plugs the container filled with the content by the filling device, the method comprising: a step of sterilizing the preform by the preform sterilizer; a step of blow-molding the preform by the blow-molding device to manufacture the container; a step of filling the container with a culture medium by the filling device without sterilizing the container by the container sterilizer; a step of plugging the container by the plugging device; a step of verifying how much microorganism survive or propagate in the culture medium in the container; and a step of adjusting a degree of sterilization in the container sterilizer on the basis of a verification result, wherein the step of adjusting the degree of sterilization in the container sterilizer includes a step of setting a sterilization performance of the container sterilizer such that a value ΣR 2 becomes (H 0 - ΣR 1 + ΣI) - FSO or more, wherein H 0 is an initial microorganism level of the preform, ΣR 1 is a microorganism reducing level on the preform by the preform sterilizer, ΣI is an increase in level of microorganism on the preform or the container between immediately after the preform sterilizer and immediately before the container sterilizer, ΣR 2 is a microorganism reducing level on the container by the container sterilizer, and FSO is a target value of a microorganism level on the container after the container passes through the container sterilizer. a step of sterilizing the preform by the preform sterilizer; a step of blow-molding the preform by the blow-molding device to manufacture the container; a step of filling the container with a culture medium by the filling device without sterilizing the container by the container sterilizer; a step of plugging the container by the plugging device; a step of verifying how much microorganism survive or propagate in the culture medium in the container; and a step of adjusting a degree of sterilization in the container sterilizer on the basis of a verification result, wherein the step of adjusting the degree of sterilization in the container sterilizer includes a step of setting a sterilization performance of the container sterilizer such that a value ΣR 2 becomes (H 0 - ΣR 1 + ΣI) - FSO or more, wherein H 0 is an initial microorganism level of the preform, ΣR 1 is a microorganism reducing level on the preform by the preform sterilizer, ΣI is an increase in level of microorganism on the preform or the container between immediately after the preform sterilizer and immediately before the container sterilizer, ΣR 2 is a microorganism reducing level on the container by the container sterilizer, and FSO is a target value of a microorganism level on the container after the container passes through the container sterilizer.