This disclosure is directed to widen an adjustable range of the spectral linewidth of laser light output from a laser apparatus. This laser apparatus may include: (1) an excitation source configured to excite a laser medium in a laser gain space, (2) an optical resonator including an output coupler arranged on one side of an optical path through the laser gain space and a wavelength dispersion element arranged on the other side of the optical path through the laser gain space, and (3) a switching mechanism configured to switch a beam-width magnification or reduction factor by placing or removing at least one beam-width change optical system for expanding or reducing a beam width in or from an optical path between the laser gain space and the wavelength dispersion element or by inverting orientation of the at least one beam-width change optical system in the optical path.