A charging voltage Vosc applied to a main capacitor C0 disposed in an
oscillating high-voltage pulse generator 12 of an oscillating laser 100
is subject to constant control such that a pulse energy Posc of the
oscillating laser 100 becomes a lower limit energy Es0 or more of an
amplification saturation region. And, a charging voltage Vamp applied to
a main capacitor C0 disposed in an amplifying high-voltage pulse
generator 32 of an amplifying laser 300 is controlled, and pulse energy
Pamp of the amplifying laser 300 is determined as target energy Patgt.
Thus, the pulse energy of a two-stage laser is controlled to stabilize
the pulse energy.