A laser processing machine comprising: a beam parameter product variable device configured to vary beam parameter products of a laser beam emitted by a laser oscillator ; and characterized by a beam diameter variable device configured to change a beam diameter of the laser beam emitted by the beam parameter product variable device , wherein the beam parameter product variable device sets beam parameter products of the laser beam to a predetermined value, the beam diameter variable device includes: a first lens that is movable in an optical axis direction and having a positive focal length, and configured to convert divergent light of a laser beam emitted from an emission end of the laser beam into convergent beam light; and a second lens that is movable in the optical axis direction and having a negative focal length on which the convergent light is incident, the second lens is disposed at a position, which is shifted from a position where the convergent light is focused toward the first lens side by the same distance as the focal length of the second lens according to a position of the first lens in the optical axis direction, and is configured to convert the convergent light into parallel light, and the laser processing machine further comprises a third lens having a positive focal length, configured to focus the laser beam emitted from the beam diameter variable device , and to irradiate a plate material (W1) with the focused laser beam. a beam parameter product variable device configured to vary beam parameter products of a laser beam emitted by a laser oscillator ; and characterized by a beam diameter variable device configured to change a beam diameter of the laser beam emitted by the beam parameter product variable device , wherein the beam parameter product variable device sets beam parameter products of the laser beam to a predetermined value, the beam diameter variable device includes: a first lens that is movable in an optical axis direction and having a positive focal length, and configured to convert divergent light of a laser beam emitted from an emission end of the laser beam into convergent beam light; and a second lens that is movable in the optical axis direction and having a negative focal length on which the convergent light is incident, a first lens that is movable in an optical axis direction and having a positive focal length, and configured to convert divergent light of a laser beam emitted from an emission end of the laser beam into convergent beam light; and a second lens that is movable in the optical axis direction and having a negative focal length on which the convergent light is incident, the second lens is disposed at a position, which is shifted from a position where the convergent light is focused toward the first lens side by the same distance as the focal length of the second lens according to a position of the first lens in the optical axis direction, and is configured to convert the convergent light into parallel light, and the laser processing machine further comprises a third lens having a positive focal length, configured to focus the laser beam emitted from the beam diameter variable device , and to irradiate a plate material (W1) with the focused laser beam. <EOS>