Provided are an antiviral agent and an antiviral food that are novel ways to use an extract from a wild watermelon. The antiviral agent and the antiviral food each contain, as an active ingredient, an extract from a wild watermelon, and are used for prevention or treatment of an infectious disease caused by a virus. For example, the virus is an RNA virus, and is selected from the group consisting of influenza viruses, rotaviruses, and noroviruses. Further, for example, the extract of a wild watermelon is a fruit juice (extract) obtained from the fruit of a wild watermelon.
