This paper deals with the effect of the direct heating method(DHM) for straightening the micro wire. Straightened micro wires have been widely used in the fields of the medicine and the semi-conductor. We have developed a micro wire straightening system by using the direct wire heating method. To controling the tension of the micro wire during the heating and straightening process, a precision tension sensor was set up. In order to avoid the surface oxidation during the heating process, the argon inert gas was supplied to the vicinity of the wire. And, this paper shows the correlation between the tension and the current when arson gas supplied to the tungsten wire. Through several experiments, the optimal tension and current were found. Also, higher straightness $({approx}1{mu}m/1000{mu}m)$ and roundness$(<{Phi}{pm}2{mu}m/100{mu}m)$ founded when $500{mu}600gf$ tension and 1.5 ampere.