a pilot fire port 8 attached to the vicinity of cutting tip 2 a needle valve 10 which extends behind the rear face of the block under the handle is capable of optionally setting the mixed gas flowrate passing through the interior of the mixed gas channel 6 by means of the knob 11 fig5 indicates a pilot gas control valve 12a which is mounted in a chamber formed in the block adjacent a rear face thereof and connected to the branched gas passage 3b an ignition lever button 13 protrudes above the upper face of handle section 1a and is structured so that when it is pushed in the pilot gas control valve 12a is opened by the spindle 14 and can be automatically returned by a return spring 12b a piezoelectric type ignition unit 15 discharges electricity between electrodes 8a of the pilot fire port 8 is mounted in a chamber formed in the manifold block opening to the upper face of the block and when the pilot gas control valve 12a is opened by use of the said ignition lever 13 a jet gas valve 16 is mounted in a chamber formed in the manifold block opening to the upper face of the block and controlled by a knob 17 fitted to the handle section 1a which is mounted to the branched jet gas passage or bore which interconnects oxygen passages 4a and 7 16 in order to regulate the flowrate of jet gas passing through the inside of the jet gas passage 7 a back fire preventive unit 18 is releasably.