The halogen lamps used as the light source in copying machines suffer from short service life, caused by stress of repeated elongation and contraction of the filament occurring as the lamp is turned on and off. To resolve this problem, the authors developed a new doped tungsten wire for use in high-stress halogen lamps. Lamp life was improved by using a potassium content of 85 to 110 ppm, achieving a tensile strength at room temperature to 2000 to 3000 N/mm2 while reducing working strain by heat treatment during working, and increasing the tensile strength at 2773K to over 55 N/mm2 in a nitrogen atmosphere.