Abstract: A laser apparatus using a DC-DC converter type pulse power source generates a pulse laser output of a high peak value by utilizing the negative resistance characteristic of a laser discharge tube. The peak value, pulse width, period of the pulse output are adjustable. The apparatus is capable of producing a continuously oscillating laser light; capable of operating always with approximately maximum efficiency for any value of the laser output. The power source device for the laser apparatus permits adjustment of the pulse width and period of the pulse laser output without any adverse effect on the efficiency of the laser apparatus.