Surface-treated steel sheet

A surface-treated steel sheet comprising:

• a steel sheet;
• a zinc-based plated layer formed on a surface of the steel sheet;
• and
• a chemical conversion treatment layer formed on a surface of the zinc-based plated layer,
• wherein the chemical conversion treatment layer contains Si, C, O and P,
• the chemical conversion treatment layer has an average C concentration across the entire chemical conversion treatment layer of 20.0 mass % or more, an average O concentration across the entire chemical conversion treatment layer of 15.0 mass % or more, an average Si concentration across the entire chemical conversion treatment layer of 10.0 mass % or more, and an average P concentration across the entire chemical conversion treatment layer of 0.10 mass % or more,
• when t is a thickness of the chemical conversion treatment layer, an area starting from a surface of the chemical conversion treatment layer and ending at a position of t/10 from the surface of the chemical conversion treatment layer in a thickness direction is a surface layer region, an area starting from the position of 9t/10 from the surface of the chemical conversion treatment layer in the thickness direction and ending at an interface between the chemical conversion treatment layer and the zinc-based plated layer is an interface side region, and a region sandwiched between the surface layer region and the interface side region is an intermediate region,
• a maximum value of a mass % P concentration of the surface layer region is 1.5 times to 5.0 times an average mass % P concentration of an intermediate region.