PURPOSE: To obtain a convenient burner unit for small fire power having a wide range of combustion capacity, by providing a means to control the number of openings which contain balls which are movable in a gas feeding passage, and of which number of gas feeding ports can be increased and decreased, as well as providing a number of gas feeding to the burner unit.

CONSTITUTION: The burner unit is provided with a passage member 12 in the lower part of a casing 11, and a heat exchanger 13 consisting of a bended tube in the upper part. The passage member 12 is made of a circular tube spirally bended, having a spiral passage 121 inside of it. The upper end of the passage 121 is sealed up, while the lower end is connected to a gas feeding port 15. In addition, holes 122 as gas feeding ports are formed in a number of places of which height are different to each other. Balls 16, which are able to be rolled round contacting with the entire internal circumference of a passage, are put into the passage 121. The number of openings of holes 122 are controlled by balls 16 pushed up to the position where the pressure of fed gas from a gas feeding port 15 and the weight of balls 16 come to be balanced to each other.