In a laser processing apparatus including an ultra-short pulse laser a focusing optical system and processing a work by projecting a beam delivered through the focusing optical system on to the work, the focusing optical system has at least a pair of diffractive surface and a refractive surface, and chromatic aberration is corrected or chromatic aberration and pulse extension are corrected by making use of the diffractive dispersions due to and the diffractive surface the refractive dispersion due to of the refractive surface. With this arrangement, chromatic aberration is corrected or both chromatic aberration and pulse expansion are corrected in the processing with the ultra-short pulse laser and thereby improve the practical use and value of the processing by improving its accuray, qualiy and speed.