A coated steel sheet including a steel sheet and a coating layer provided on at least part of the surface of the steel sheet, in which the coating layer has a predetermined chemical composition in terms of % by mass, and the coating layer has a granular Mg2Sn phase-containing structure in an area fraction of from 5 to 65%, and a structure containing a solid solution of Zn and Al, and the granular Mg2Sn phase-containing structure is a structure constituted with a Zn phase and a granular Mg2Sn phase having a crystal grain size of less than 1 μm dispersed in the Zn phase.