A core material including a core and a solder plating layer of a (Sn—Bi)-based solder alloy made of Sn and Bi on a surface of the core. Bi in the solder plating layer is distributed in the solder plating layer at a concentration ratio in a predetermined range of, for example, 91.7% to 106.7%. Bi in the solder plating layer is homogeneous, and thus, a Bi concentration ratio is in a predetermined range over the entire solder plating layer including an inner circumference side and an outer circumference side in the solder plating layer.