Using a laser source unit, a plurality of wavelengths are switched at a high speed without increasing a rotation speed of a birefringent-filter. A Q switch and a birefringent filter are inserted into an optical resonator including a pair of mirrors facing each other with a laser rod interposed therebetween. The birefringent-filter changes an oscillation wavelength of the optical resonator in association with rotational displacement. Driving means reciprocatively rotates the birefringent-filter in a predetermined range including a discontinuous point of change characteristics of a transmission wavelength for the rotational displacement. An emission control unit irradiates the laser rod with excitation light from a flash lamp, and then turns on the Q switch at a timing when a rotational displacement position of the birefringent-filter is set to a position corresponding to the wavelength of the pulse laser beam to be emitted, to cause the pulse laser beam to be emitted.
