Using a laser source unit, pulse laser beams having a plurality of wavelengths is switched and emitted. A Q switch is inserted into an optical resonator including a pair of mirrors which face each other with a laser rod interposed therebetween. A wavelength selection means includes a plurality of band pass filters having different transmission wavelengths, and selectively inserts the plurality of band pass filters into a light path of the optical resonator. A trigger control circuit controls driving means that drives the wavelength selection means so that the band pass filters inserted into the light path of the optical resonator are switched at a predetermined switching speed. In addition, the trigger control circuit causes the laser rod to be irradiated with excitation light from a flash lamp, and then turns on the Q switch at a timing when the wavelength selection means inserts the band pass filter.
