A metallic copper and resin composite body manufacturing method of forming a copper wiring layer that forms an inner layer circuit, establishing an insulating layer with a resin on said wiring layer, forming via holes which expose the copper surface under the insulative layer, and depositing a metal on the copper surface that is exposed at the bottom of the via holes. The method includes a step of: removing copper oxide which forms on the surface of the copper that is exposed in the bottom of the via holes using a phosphoric acid aqueous solution with a pH between 1 and 3. The method suppresses haloing is and via holes with excellent solder bonding are formed.