A basic study was carried out to find out the optimal heating and cutting conditions for hot turning of difficult-to-cut materials with YAG laser. A carbon steel of S45C for machine structural use was used to examine the effects of local heating on its roachinability. The machined surface roughness against cutting temperature and the relation between cutting temperature and cutting speed were examined experimentally. Because of the lower laser power of not more than 162 W, the calculated average temperature rise in the cutting region reached less than 70 K, which was not effective to decrease the cutting force. In the cutting speed range where the marked formation and growth of built up edge was appeared, however, about 40 K of the calculated average temperature rise in the cutting region due to laser beam irradiation was effective to improve the surface roughness. In the cutting temperature range of 950 to 1200 K where the built up edge should be disappeared, the surface roughness was less than that in the temperature range of 500 to 950 K and was not affected by the cutting temperature. In the higher cutting temperature range, the slope of cutting temperature against cutting speed was decreased to 50〜75% of that in the lower temperature range.