A surface-treated steel sheet includes a chemical conversion coating with a thickness of 3.0 μm or less, the chemical conversion coating being placed on a surface of a hot-dip Zn—Al alloy coated steel sheet including a hot-dip Zn—Al alloy coating film containing Al: more than 1.0 mass % and 15 mass % or less, a balance being Zn and inevitable impurities. The chemical conversion coating contains AlH2P3O10.2H2O and a compound containing one or more elements selected from Mg, Ca, and Sr such that a sum of contents of AlH2P3O10.2H2O and the compound is 3.0 mass % to 50 mass %.