A burner (20) includes a first tube portion (30) formed with an ejection port (32) that ejects combustion gas; a second tube portion (40) that extends in the first tube portion (30) toward the ejection port (32) and to which gaseous mixture flows in from a side opposite to the ejection port (32); a third tube portion (50) that is arranged in the first tube portion (30) and internally inserted with the second tube portion (40) and that includes an open end positioned on the ejection port (32) side; a closing portion (51) that closes the open end; a coupling wall portion (41) that closes a gap between the first tube portion (30) and the second tube portion (40); a partition wall (55) that is coupled to the first tube portion (30) and the third tube portion (50), the partition wall (55) being formed with a communication path (56) that communicates a side opposite to the ejection port (32) with the ejection port (32) side with respect to the partition wall (55); and an igniting portion (62) that is arranged on the ejection port (32) side with respect to the partition wall (55) and that ignites the gaseous mixture.