Provided is a line beam forming device that can divide a laser beam into beam segments in a first direction (y-axis) perpendicular to the traveling direction (z-axis) of the laser beam, and arrange and emit the beam segments with regular intervals in a second direction (x-axis) perpendicular to the traveling direction of the laser beam, using a single mirror set composed of a plurality of mirrors. The line beam forming device of the present invention can be used for an excimer laser which is a multimode laser beam generator with high beam divergence, a high-power DPSS laser, or a laser diode, can obtain high-density energy by condensing beams, can obtain a beam profile having uniform intensity in both of a long axis and a short axis, and can combine a plurality of laser beams without being influenced by the properties of an incident beam.