The end of steel bar specimens with various diameter have been heated by mean of oxy-acetylene tips (capacity : 500;) with single and multi nozzles that is nearly equal to flat theamic source as is shown in Fig. 5, in order to measure the thermal efficiency of oxy-acetylene flame and the heat transfer coefficient between heated surface of bar specimen and the flame.The test results can be described as follows ;1) The heat quantity corresponded to 35% in total transfered heat quantity was given from the front or top of white cone to the specimen. This decision was based on the test results as is shown in Fig 1, 2, 4 and 7, and the result of consideration for them.2) A few matters should be studied are remained, however, the authors introduced the formulas (1) and (2) on the instantaneous and mean heat transfer coefficient between bar specimen and the front on top of white cone in the heated period. In this case, the temperature in front or top of white cone was assumed 3, 200°C.