To provide a multi-stage shot peening method capable of improving the undulation and surface roughness of a metal product by shot peening.

This method capable of minimizing, when the surface of the metal product is treated by the multi-stage shot peening, the surface roughness of the treated surface comprises the steps of shot peening under such shot peening conditions that the surface roughness or peak count value of the processed product are larger than those in the initial surface state of the product, and shot peening under such shot peening conditions that projection materials with a slower projection speed, smaller grain size, and/or lower hardness are used.