A burner comprising: a first tube having a tube end including an ejection port that ejects a combustion gas in which gaseous mixture is combusted; a second tube extending in the first tube toward the ejection port, the gaseous mixture flowing into the second tube from a side opposite to the ejection port; a third tube arranged in the first tube, the second tube is internally inserted into the third tube, the third tube including an open end positioned on the ejection port side; a closing portion (51; 82; 90) that closes the open end; a first wall portion that is coupled to an inner side surface of the first tube and an outer side surface of the second tube to close a gap between the first tube and the second tube; a second wall portion coupled to the inner side surface of the first tube and an outer side surface of the third tube, the second wall portion having a communication hole that communicates a side opposite to the ejection port with respect to the second wall portion with the ejection port side; an air supplying passage for supplying air; and an igniting portion that is arranged on the ejection port side with respect to the second wall portion and that is configured to ignite the gaseous mixture, characterized in that: the first tube includes an extended part extending toward the side opposite to the ejection port from a coupling portion of the first tube with the first wall portion; the extended part defines a space that is configured to receive fuel and air; and the extended part has first introduction ports that, in use, introduce air supplied through the air supply passage into the extended part and swirling flow generating portions that, in use, generate a swirling flow of the air supplied through the air supplying passage in the extended part; wherein the first tube includes: second introduction ports that are positioned in a region of the ejection port side with respect to the igniting portion, wherein the second introduction ports introduce air to a gap between the first tube and the third tube. a first tube having a tube end including an ejection port that ejects a combustion gas in which gaseous mixture is combusted; a second tube extending in the first tube toward the ejection port, the gaseous mixture flowing into the second tube from a side opposite to the ejection port; a third tube arranged in the first tube, the second tube is internally inserted into the third tube, the third tube including an open end positioned on the ejection port side; a closing portion (51; 82; 90) that closes the open end; a first wall portion that is coupled to an inner side surface of the first tube and an outer side surface of the second tube to close a gap between the first tube and the second tube; a second wall portion coupled to the inner side surface of the first tube and an outer side surface of the third tube, the second wall portion having a communication hole that communicates a side opposite to the ejection port with respect to the second wall portion with the ejection port side; an air supplying passage for supplying air; and an igniting portion that is arranged on the ejection port side with respect to the second wall portion and that is configured to ignite the gaseous mixture, characterized in that: the first tube includes an extended part extending toward the side opposite to the ejection port from a coupling portion of the first tube with the first wall portion; the extended part defines a space that is configured to receive fuel and air; and the extended part has first introduction ports that, in use, introduce air supplied through the air supply passage into the extended part and swirling flow generating portions that, in use, generate a swirling flow of the air supplied through the air supplying passage in the extended part; wherein the first tube includes: second introduction ports that are positioned in a region of the ejection port side with respect to the igniting portion, wherein the second introduction ports introduce air to a gap between the first tube and the third tube. the first tube includes an extended part extending toward the side opposite to the ejection port from a coupling portion of the first tube with the first wall portion; the extended part defines a space that is configured to receive fuel and air; and the extended part has first introduction ports that, in use, introduce air supplied through the air supply passage into the extended part and swirling flow generating portions that, in use, generate a swirling flow of the air supplied through the air supplying passage in the extended part; wherein the first tube includes: second introduction ports that are positioned in a region of the ejection port side with respect to the igniting portion, wherein the second introduction ports introduce air to a gap between the first tube and the third tube. second introduction ports that are positioned in a region of the ejection port side with respect to the igniting portion, wherein the second introduction ports introduce air to a gap between the first tube and the third tube.