PURPOSE: To easily obtain a laser light with a short pulse width by preventing the influence that, just after high frequency current if injected, a injection current effectiveness into the photoactive layer is reduced to make to reactive current large due to the capacity of a semiconductor laser element.

CONSTITUTION: A separation groove 17 if formed on a p-type clad layer 15, a cap layer 16 laminated on a multiple quantum well layer 14 as a photoactive layer, an electrode 18 is provided on the cap layer 16 on one side of the separation groove 17, the multiple quantum well layer 14 on the side where the electrode 18 is not arranged is made function as a light-absorption region 14a, the oscillated wavelength is shifted to the short wavelength side with elapsed time, and the laser light is made emitting via a wavelength selection element 2 only at the time where the wavelength of the laser light agrees with the selected wavelength.