PROBLEM TO BE SOLVED: To provide a water-resistant influenza virus infection inhibitor which can prevent the spread of influenza infection by eliminating or reducing the infectability of influenza viruses through adsorption of the influenza viruses.SOLUTION: The influenza virus infection inhibitor includes a cross-linked body obtained by cross-linking a monomer having at least one of substituents having structural formulae represented by general formulae (1)-(3) and a monomer having a carboxyl.