It is an object of the present invention to provide a copper-based bonding wire whose material cost is low, having excellent ball bondability, reliability in a heat cycle test or reflow test, and storage life, enabling an application to thinning of a wire used for fine pitch connection. The bonding wire includes a core material having copper as a main component and an outer layer which is provided on the core material and contains a metal M and copper, in which the metal M differs from the core material in one or both of components and composition. The outer layer is 0.021 to 0.12 μm in thickness.