An injection locking type or MOPA type of laser device capable of always providing stable output energy and wavelength is provided. For this purpose, the laser device includes an oscillator for exciting laser gas by oscillator discharge and oscillating seed laser light with band-narrowed wavelength, an amplifier for amplifying the seed laser light by amplification discharge to emit amplified laser light, a delay circuit for setting at least one of a delay time from light emission of the seed laser light to light emission of the amplified laser light, and a delay time from start of the oscillator discharge to start of the aforementioned amplification discharge, and a delay time compensation circuit for performing compensation of the delay circuit so that the delay time becomes an optimal delay time.