A laser apparatus includes: a laser oscillator including a wavelength adjuster and configured to output pulse laser light having a center wavelength adjusted by the wavelength adjuster; a spectrum monitor configured to generate data on a spectrum of the pulse laser light; and a processor configured to control the wavelength adjuster in such a way that the center wavelength of the pulse laser light changes in accordance with a target wavelength that periodically changes to each of multiple values including first and second wavelengths, calculate a first spectral linewidth from data on spectra of multiple pulses each having the first wavelength as the target wavelength, and calculate a second spectral linewidth from data on spectra of multiple pulses each having the second wavelength as the target wavelength.