Abstract: The present invention has revealed that an antiviral agent containing a serine protease such as subtilisin, nattokinase, and trypsin has an effect of inactivating non-envelope type viruses, and that combining such an antiviral agent containing a serine protease with a cationic polymer enhances the inactivation effect of the antiviral agent against non-envelope type viruses. As a result, an antiviral agent that is highly safe, that has a high virus inactivation ability, and that contains a component that is inexpensive in terms the manufacturing cost and a cationic polymer, was discovered.