1. A laser apparatus comprising: a laser chamber filled with a laser gain medium; a pair of electrodes disposed in the laser chamber; a charger configured to apply a charge voltage for causing a discharge to occur between the pair of the electrodes; a pulse power module configured to covert the charge voltage applied by the charger into a short pulsed voltage, and apply the short pulsed voltage between the pair of the electrodes; and a controller configured to calculate input energies Ein applied to the pair of the electrodes based on the charge voltage, calculate an integration value Einsum of the input energies Ein by integrating the calculated input energies Ein, and determine whether the integration value Einsum exceeds an integration lifetime value Einsumlife of input energy or not.