A He-Cd ion laser of the type having a series of anodes open to the interior of a hollow cathode, a series of metal chambers containing a supply of Cd to be vaporized, and a heater for heating the metal chambers for vaporizing the Cd supply. For holding constant the Cd vapor pressure within the hollow cathode and, in consequence, the intensity of the output beam, an electric control system is provided which comprises a constant current regulator connected to each anode for supplying a constant current thereto, and a heater control circuit for controlling the magnitude of a current fed to the metal chamber heater so as to hold the output voltage of each constant current regulator equal to a reference voltage.