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 . <EOS>