Provided are: a vaccine against IL-17A, said vaccine using a polypeptide as an immunogen, and said polypeptide including the amino acid sequence shown in SEQ ID NO: 1 or including a non-human mammal derived amino acid sequence corresponding to SEQ ID NO: 1; and a prophylactic or therapeutic agent, or the like, for diseases to which IL-17A relates as an exacerbating factor, said prophylactic or therapeutic agent including the vaccine.