Abstract: An improved incomplete combustion preventing gas burner is disclosed, the improvement comprising: a venturi having a narrow passage and installed downstream of a mixing room in such a manner that the mixed combustible gas from the mixing room should be spouted with a high velocity through the flame holes, and a V shaped guide portion provided on the mixed combustible gas path leading from the mixing room to the flame holes. Thus, if an unstable mixing ratio occurs in the mixing room to cause an incomplete combustion, a lifting phenomenon for the flame is induced through the utilization of the high velocity of the mixed combustible gas, so that the thermal interaction between the flame 5 and the thermo-electric couple 7 should be halted, and that the combustible gas supply should be blocked, thereby extinguishing the flame.