A cooking device comprising a cavity providing a cooking chamber; and a burner provided in the cavity to heat food in the cooking chamber, wherein the burner comprises: a supply part supplying a gaseous fuel mixed with air; and at least one tubular combustion part that burns the mixed gaseous fuel; the at least one tubular combustion part has an open curve shape with a first end receiving the mixed gaseous fuel and the other end closed, wherein the at least one combustion part comprises: a plurality of straight portions (521, 522, 523, 524) spaced apart from each other; and one or more connection portions (531, 532, 533) connecting the straight portions (521, 522, 523, 524) wherein the straight portions (521, 522, 523, 524) are in parallel with each other and the connection portion (531, 532, 533) is round, wherein each of the straight portions (521, 522, 523, 524) is provided with a plurality of flame holes (541, 542, 543, 544) for generating flames, characterized in that the flame hole (541, 542, 543, 544) of the straight portion (521, 522, 523, 524) distant from the supply part along a flow path of the mixed gaseous fuel is greater than the flame hole (541, 542, 543, 544) of the straight portion (521, 522, 523, 524) close to the supply part along the flow path of the mixed gaseous fuel, that the connection portion (531, 532, 533) including inner connection portions and out connection portions, wherein the inner connection portion comprises a plurality of flame holes (545, 546, 547) that transfers a flame between adjacent two of the straight portions, and that a distance between the flame holes (545, 546, 547) of the connection portion (531, 532, 533) is greater than a distance between the flame holes (541, 542, 543, 544) of the straight portion (521, 522, 523, 524). a supply part supplying a gaseous fuel mixed with air; and at least one tubular combustion part that burns the mixed gaseous fuel; the at least one tubular combustion part has an open curve shape with a first end receiving the mixed gaseous fuel and the other end closed, wherein the at least one combustion part comprises: a plurality of straight portions (521, 522, 523, 524) spaced apart from each other; and one or more connection portions (531, 532, 533) connecting the straight portions (521, 522, 523, 524) a plurality of straight portions (521, 522, 523, 524) spaced apart from each other; and one or more connection portions (531, 532, 533) connecting the straight portions (521, 522, 523, 524) wherein the straight portions (521, 522, 523, 524) are in parallel with each other and the connection portion (531, 532, 533) is round, wherein each of the straight portions (521, 522, 523, 524) is provided with a plurality of flame holes (541, 542, 543, 544) for generating flames, characterized in that the flame hole (541, 542, 543, 544) of the straight portion (521, 522, 523, 524) distant from the supply part along a flow path of the mixed gaseous fuel is greater than the flame hole (541, 542, 543, 544) of the straight portion (521, 522, 523, 524) close to the supply part along the flow path of the mixed gaseous fuel, that the connection portion (531, 532, 533) including inner connection portions and out connection portions, wherein the inner connection portion comprises a plurality of flame holes (545, 546, 547) that transfers a flame between adjacent two of the straight portions, and that a distance between the flame holes (545, 546, 547) of the connection portion (531, 532, 533) is greater than a distance between the flame holes (541, 542, 543, 544) of the straight portion (521, 522, 523, 524).