In order to obtain a laser processing device with which the beam dispersion angle can be controlled adequately using a reflected beam expander mechanism wherein the light path configuration is not particularly complex, and with which a material to be processed can be illuminated with laser light that is aplanatic and has the desired beam diameter, this laser processing device is equipped with: a laser oscillator (1); a processing table (2); a transmission optical system that transmits laser light (L) emitted from the laser oscillator (1) to the processing table (2); a processing head (4) that focuses the laser light (L) transmitted through the transmission optical system and illuminates the material to be processed with the laser light; a movement means (5) that changes the relative positions of the material to be processed and the laser light (L) with which the material to be processed is illuminated; and a variable-curvature spherical mirror (67). The transmission optical system is equipped with a reflected beam expander mechanism (6) that parallelizes and expands the laser light from the laser oscillator (1), and the reflected beam expander mechanism (6) is constructed so as to include a spherical mirror (63), and a concave mirror (62) for which the two orthogonal axes have different curvatures.
