The generatrix directions of cylindrical lenses 11a and 11b are perpendicular to the optical axis, and are perpendicular to each other. As a result, the optical system combining the cylindrical lenses 11a and 11b can achieve the same optical effect as a spherical lens. This system is characterized by the fact that since the respective lenses are cylindrical lenses, there is no shift in the optical axis even if the lenses are moved in the generatrix direction. For example, in cases where scratches on the lenses have become conspicuous, the useful life of the laser device can be extended by moving the lenses in the generatrix direction (direction indicated by the arrow) by means of a moving mechanism (not shown in the figures), e.g., a stage equipped with a micrometer, and using unused portions of the lenses.