ANTIVIRAL AGENT AND ANTIVIRAL FOOD Provided are an antiviral agent and an antiviral food as novel methods for utilizing a Euglena-derived material. The antiviral agent and antiviral food, both comprising a Euglena-derived material as an active ingredient, are to be used for preventing or treating an infectious disease caused by an envelope-free RNA virus. Examples of the envelope-free RNA virus include rotaviruses belonging to Reoviridae. Examples of the Euglena-derived material include Euglena, a hot water extract of Euglena, paramylon and an alkali-treated paramylon. FIG. 36