A guide laser beam that has an optical axis and a beam diameter substantially equivalent to those of a driver pulsed laser beam is introduced into an amplification system that amplifies a laser beam that is output from a driver laser oscillator. The guide laser beam is output from a laser device as a continuous light, and is introduced into a light path of the driver pulsed laser beam via a guide laser beam introduction mirror. A sensor detects an angle (a direction) of a laser beam and a variation of a curvature of a wave front. A wave front correction controller outputs a signal to a wave front correction part based on a measured result of a sensor. The wave front correction part corrects a wave front of a laser beam to be a predetermined wave front according to an instruction from the wave front correction controller.