It is an object of the present invention to provide an antibody that inhibits infection of cells with a norovirus, wherein the antibody is a nanoantibody comprising a polypeptide described in the following (a), (b), or (c), and inhibiting infection of intestinal cells with HuNoV GII.3 and/or HuNoV GII.4:(a) a polypeptide consisting of the amino acid sequence as set forth in SEQ ID NO: 1, SEQ ID NO: 5, SEQ ID NO: 9, or SEQ ID NO: 13；(b) a polypeptide consisting of an amino acid sequence comprising a substitution, deletion, insertion and/or addition of one or several amino acids with respect to the amino acid sequence as set forth in SEQ ID NO: 1, SEQ ID NO: 5, SEQ ID NO: 9, or SEQ ID NO: 13； and(c) a polypeptide consisting of an amino acid sequence having a sequence identity of 80% or more to the amino acid sequence as set forth in SEQ ID NO: 1, SEQ ID NO: 5, SEQ ID NO: 9, or SEQ ID NO: 13.
