Disclosed is a high-quality aptamer for IL-17, and that is, for example, an aptamer having inhibitory activity against IL-17, a compound that contains a functional substance (such as an affinity substance, a labeling substance, an enzyme, a drug delivery medium, or a drug) and an aptamer having binding activity or inhibitory activity against IL-17, or a medicine, diagnostic agent, or labeling agent that contains an aptamer having binding activity or inhibitory activity against IL-17, or a compound of said aptamer and a functional substance.