Injection nozzle 7 and electrode rods 8 and 9 (ignitor) are surrounded by double-cylinder flame stabilizer 10. Toroidal blocking plate 13 closes between inner and outer cylinders 11 and 12 of the stabilizer at its distal end whose proximal end is connected with line 15 for introducing combustion air 14 to between the cylinders. Inflow holes 16 are formed throughout the inner cylinder at its proximal end. Peripheral fins 17 are formed peripherally on the inner cylinder radially inwardly through cutting and bending-up at positions shifted from the inflow holes toward the distal end of the inner cylinder such that combustion air is introduced from circumferentially to form swirling flow inside the inner cylinder. End fins 18 are formed on the blocking plate in fuel injection direction through cutting and bending-up such that combustion air is discharged circumferentially to form swirling flow around flame 21.