PURPOSE: To form combustion cylinder itself in structure doubling as an expansion cavity type silencer, and to inhibit air column vibration having resonance frequency by a construction wherein the combustion cylinder is divided into two upper and lower chambers by a holding plate, and an inserting pipe, upper and lower sections thereof are opened, is disposed at the center.

CONSTITUTION: The holding plate 3, which is mounted into the combustion cylinder proper 1 and supports the inserting pipe 2, upper and lower sections thereof have openings 21, also fills the role of a partition wall dividing the combustion cylinder 1 into the two sections of the upper and lower chambers 12, 13. A burner 5 is housed in a combustion chamber 4, and a blast pipe 6 supplies air for combustion. The upper and lower chambers 11, 12 of the combustion cylinder are formed as the silencer S doubling as a double extension expansion chamber through the inserting pipe 2, and the inserting pipe 2 is arranged to a knot section of the distribution of sound pressure shaped in the combustion cylinder 1. Accordingly, the distribution of sound pressure having antiphase is formed, the variation of pressure is removed through the mutual interference, and feedback to a lower section of a flame surface is eliminated, thus extinguishing the air column vibration having resonance frequency.