The present invention relates to a combustor which secondly burns the incomplete combustion gas generated by a first combustion conducted in a dry gasifier to achieve a complete combustion, and which comprises: an ignition chamber (20) in communication with a gas outlet (11) for discharging gas burnt firstly in a dry gasifier (1) and equipped with a burner (21); a combustion chamber (40) which is subsequently in communication with the ignition chamber (20) via a passage (30) having a cross-sectional area smaller than that of the ignition chamber (20), and which has a flame outlet (41); and two circulation paths (50, 60) for placing the ignition chamber (20) and the combustion chamber (40) in communication. The circulation paths (50, 60) are combined into a unitary body such that one end of the combined body has a first connection portion (52) for connecting to the combustion chamber (40), and the other end of the combined body has a second connection portion (53) and a third connection portion (63) spaced apart from each other by a predetermined angle to be connected to the ignition chamber (20). By using the thus-configured combustor, the incomplete combustion gas discharged through the plurality of circulation paths (50, 60) is returned to the ignition chamber (20) from the combustion chamber (40), and a vortex flow is formed within the ignition chamber (20) to induce a complete combustion, and the steam supplied by the combustion chamber (40) is combined with carbon dioxide to produce a synthesized gas.