A laser beam heat treatment for a metal wire has improved incidence and processing conditions so as to achieve efficient surface heat treatment with a circumferentially averaged laser beam flux and with remarkably enhanced fatigue strength in a high speed heat treatment. The method and apparatus is characterized by forming a cone shaped mirror of circular or polygon cross section having a peak angle in a range of 5.degree. to 20.degree. and interior mirror surface, the cone shaped mirror defining an opening having a diameter greater than the diameter of the metal wire in a range of 0.2 to 2 mm, feeding the metal wire having a diameter less than or equal to 1 mm through the cone shaped mirror along the center axis thereof, irradiating a laser beam with an incident angle including an angular deflection with respect to the center axis of the cone shaped mirror in a range of .+-.10.degree. resulting in multiple reflection of the laser beam between the interior mirror surface and the surface of the fed metal wire.