Si material, which has been considered to be very brittle, and hard to bend, is heated to at least its brittle-ductile transition temperature. A bending moment is applied to a heated portion of the Si material so that a slip deformation is generated. Whereby it is possible to perform bending, and to greatly improve a degree of freedom for machining the Si material. The Si material has a brittle-ductile transition temperature which transfers from a brittle to a ductile state at its brittle-ductile transition temperature. At the transition temperature or more, the Si material is in a state that a slip can to be generated between its crystals in response to a bending torque applied thereto. Thus, when a bending moment is applied to the heated portion of the Si material which is heated to the transition temperature or more, a slip is generated between lattices or between crystal grains in the heated portion, so that the Si material is deformed.