To enhance the accuracy of profile, when surface-machining a V-shaped or U-shaped groove in the light receiving side surface of the substrate for a solar cell employing a crystalline Si substrate, by machining the surface of the substrate using a diamond wire saw.

A mechanism integrating a supplying wire bobbin 22 and a collecting wire bobbin 23 is set such that a wire 24 is located on a crystalline Si substrate 21. The wire 24 is then traveled while being fed by turning the supplying wire bobbin 22 and the collecting wire bobbin 23. It is then lowered onto the Si substrate 21 and a groove is cut by abutting a wire saw against the Si substrate 21. According to the method, machining is stabilized while suppressing friction of fixture and the accuracy of profile can be enhanced and sustained easily at a high level.