PURPOSE: To reduce the influence of variations of the pressure inside an evaporation chamber upon a secondary air intake port and prevent the generation of a back- fire by providing a plurality of primary air intake holes at a front wall of the evaporation chamber.

CONSTITUTION: The secondary air intake port 45 and flame discharging port 31 are provided in the outside peripheral surface of the evaporation chamber 55 partitioned within a jet-type burner 13, and a plurality of primary air intake holes 71 are provided in the front wall 47 of the evaporation chamber 55 at which wall a fuel jetting device 61 is provided. Accordingly, the influence of the variations of the pressure inside the evaporation chamber 55 upon the port 45 is reduced and the generation of the back-fire can be prevented.