The purpose of the present invention is to provide a coating structure material having excellent magnesium erosion resistance, which provides resistance to erosion caused by molten magnesium and molten magnesium alloys. The present invention pertains to a coating structure material wherein a cobalt-based alloy coating layer is formed on a nickel/cobalt-based alloy substrate. The cobalt-based alloy coating layer contains, in mass%, not more than 20% nickel, not less than 42% cobalt, not more than 2.8% silicon, and not more than 3.5% iron.