PURPOSE: To perform brazing without the need for a manual operation and to enable automation by ejecting a heating flame from the tip of a torch to preheat a work then throttling the heating flame and delivering a solder bar from the central hole at the tip of the torch thereby brazing the work.

CONSTITUTION: When the operator turns on the start switch of a robot 5, a solenoid valve 14 of a gaseous acetylene supply circuit 1 and solenoid valves 24a, 24b of the auxiliary circuit 2B and main circuit 2A of an oxygen supply circuit 2 open. The gaseous acetylene mixed with a pulverized flux and the gaseous oxygen of the amt. enough for preheating are supplied into a torch 4 to preheat a work 6. When the surface of the work 6 attains a specified temp., the valve 24b of the circuit 2B is closed by a sensor or timer and the circuit 2 is changed over only to the circuit 2A so that the supply rate of the gaseous oxygen is throttled down to the rate adequate for brazing. A mechanism 3 for feeding a solder bar is then actuated to start feeding a solder bar 31 from the tip of the torch 4 at a prescribed speed. The robot 5 reproduces the teaching motion at the same instant. The brazing operation is thus accomplished.