A Cu—Mo substrate 10 according to the present invention includes: a Cu base 1 containing Cu as a main component; an Mo base having opposing first and second principal faces 2a, 2b and containing Mo as a main component, the second principal face 2b of the Mo base 2 being positioned on at least a portion of a principal face 1a of the Cu base 1; and a first Sn—Cu-type alloy layer 3 covering the first principal face 2a and side faces 2c and 2d of the Mo base 2, the first Sn—Cu-type alloy layer 3 containing no less than 1 mass % and no more than 13 mass % of Sn.