Abstract: A shape with a substantially perfect sphere, or a cross-sectional shape with a substantially perfect circle in a direction parallel to an advance direction of a femtosecond laser light beam, is obtained as a processed shape such as a modified shape of a worked shape. Rays of femtosecond laser light (L1, L2) are entered into lenses (16, 20), respectively, and the rays of laser light are focused inside a transparent material (100) by the lenses such that each of the optical axes of the rays has a predetermined angle. The light focus positions of the rays of femtosecond laser light are superposed inside the transparent material and the inside of the material is processed.