Provided is a surface treatment method for a surgical implant that improves fatigue strength of the surgical implant while maintaining the microscopic surface structure of the surgical implant. A surface treatment method for a surgical implant (3), including: placing an additive manufactured surgical implant (3) in a processing liquid, the surgical implant (3) including a microscopic surface structure (51) having a complete penetration area (52a) and an incomplete penetration area (52b); and causing a nozzle (15) immersed in the processing liquid to eject a cavitation jet of the processing liquid to the surgical implant (3) to remove the incomplete penetration area (52b) remaining on a surface of the surgical implant (3) and apply a compressive residual stress to the surface of the surgical implant (3).