To provide excimer laser device which can minimize variations in the exposure by eliminating a spike-like pattern of pulse energy, and perform exposure with a less number of pulses than a conventional laser.

In an excimer laser device capable of performing burst-mode oscillation, the energy amount of pulses oscillated from the excimer laser device is detected, the relationship between a discharge voltage in each pulse and the amount of energy from the start of the oscillation state is obtained based on the detection result, and the discharge voltage is controlled based on the obtained relationship, so that the energy amount in each pulse during the oscillation state is almost constant.