A laser apparatus may comprise: a laser chamber configured to include a laser gain medium; a pair of electrodes disposed in the laser chamber; an energy detector configured to measure pulse energy of laser beams outputted by discharging between the pair of the electrodes; an optical element disposed on a light path of the laser beams; and a controller configured to calculate an integration value of absorption energy at the optical element, and determine whether the integration value exceeds a lifetime integration value of the optical element based on the pulse energy of the laser beams.