The surface treatment agent for copper and copper alloys contains hydrogen peroxide, a mineral acid, an azole compound, silver ion and a halide ion. The surface treatment agent for copper and copper alloys is useful in the production of printed wiring boards in electronics industry. The surface treatment agent roughens the surface of copper and copper alloys. Particularly, the surface treatment agent can form a uniform and undulation-free roughened surface on copper-clad substrates having plated mirror surface, this having been difficult in conventional techniques, thereby significantly improving the adhesion to etching resists, solder resists, in addition, to prepregs and a resin for mounting electronic parts.