A substrate treatment method includes the steps of: supporting a substrate with a support member; arranging an extension surface such that the extension surface laterally surrounds one major surface of the substrate supported by the support member and extends continuously to the major surface of the substrate supported by the support member; rotating the substrate supported by the support member; and etching the substrate by supplying an etching liquid onto the major surface of the substrate supported by the support member, wherein the extension surface has higher affinity for the etching liquid than the major surface of the substrate supported by the support member.