An object of the present invention is 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 bonding wire is characterized in that the outer layer is 0.021 to 0.12 [mu]m in thickness; the metal M is Pd; and the outer layer is the portion containging more than 50 mol% of Pd.