A laser beam machining system including a chuck table for holding a work, and a laser beam irradiation unit for irradiating the work held on the chuck table with a laser beam, wherein the laser beam irradiation unit includes: a pulsed laser beam oscillator for oscillating a pulsed laser beam; a condenser for condensing the pulsed laser beam oscillated from the pulsed laser beam oscillator; a laser beam scanning unit disposed between the pulsed laser beam oscillator and the condenser and operative to deflect the pulsed laser beam to be inputted to the condenser; and a laser beam reshaping unit which ids disposed between the pulsed laser beam oscillator and the laser beam scanning unit and by which the energy distribution of the pulsed laser beam oscillated from the pulsed laser beam oscillator is reshaped into a top hat shape.