The present invention addresses the problem of providing a novel substance capable of interfering with various functions of integrin a4, and/or providing a novel substance capable of interfering with both integrin a4 and integrin a9. The present invention provides an integrin a4 mutant peptide having one portion of the extracellular domain of human integrin a4, and the like, and in concrete terms relates to a peptide and the like having the amino acid sequence of Sequence No. 4 through 9, and a pharmaceutical composition comprising as the active ingredient the same peptide.
