A lead pin comprising including a body having a shaft portion and a flange portion. The flange portion has at least one flat portion configured to face a connection pad and groove portions positioned to face toward the connection pad and extending from a peripheral portion toward a center portion of the flange portion, the flat portion includes extending portions extending from a center of the flange toward the peripheral portion of the flange and connected at the center of the flange, and the groove portions are tilted to become deeper toward the peripheral portion of the flange.