A lens used for a line generating optical system is provided, wherein X-axis is defined in longitudinal direction of the generated line, Y-axis is defined in width direction and Z-axis is defined in direction of the optical axis and wherein the lens has an optical surface which does not collimate the light in X-axis direction and which collimates or collects the light in Y-axis direction alone, inclination of direction of transferred tool mark with respect to X-axis being from 40 to 50 degrees in an area of 80% or more of the optical surface.