The present invention relates to an infection phylactic agent which exhibits a protective effect against influenza virus infection and is useful in the prevention and/or treatment of influenza. This infection protection agent contains, as an active component, lactadherin and/or a decomposition product obtained by treating lactadherin with a proteolytic enzyme. Having mammalian milk as the raw ingredient, this infection protection agent can be easily and economically produced and can be safely ingested on a daily basis.
