To improve adhesion between a plating film reducing contact electrical resistance and a copper alloy plate containing Mg. A copper alloy plate containing Mg of more than 1.2% by mass and 2% by mass or less and the balance Cu and inevitable impurities in a center portion in a plate thickness direction, in the copper alloy plate, a surface Mg concentration at a surface is 30% or less of a center Mg concentration at the center portion in the plate thickness direction, a surface layer portion having a depth from the surface to where a Mg concentration is 90% of the center Mg concentration is provided, and in the surface layer portion, the Mg concentration increases from the surface toward the center portion of the plate thickness direction with a concentration gradient of 0.2% by mass/μm or more and 50% by mass/μm or less.