service lever 13 extends above to the front upper face of handle section 1a and this ignition lever can be slided to the front side and if this ignition lever 13 is slid to the front side the pilot valve 12 is opened and the gas is supplied to the pilot port 8 via the pilot gas pipe 9 at the same time the piezoelectric ignition unit 15 is actuated for generating a high voltage and discharges electricity in electrodes 8a by this electric discharge a fire is set to the gas being jetted out of the pilot fire port 8 for reference the piezoelectric ignition unit is the device utilizing the officially known piezoelectric effect an the oxygen valve 16 is installed on the side of another branch channel 4c which has branched the oxygen channel 4a into the branch channel 4b and this oxygen valve 16 can be opened or closed by means of the knob 17 the downstream side of this valve 16 is interlocked with the oxygen pipe 7 a back fire preventive unit 18 is situated on upstream of the mixture chamber 5 in the gas passage 3b and is incorporated into the front area of handle section 1a in which the back fire preventive device or filter 18a made of sintered metal is incorporated.