To provide a cyclone shaped combustion device capable of remarkably decreasing NOx and being completely actually used.

Premix gas 9 obtained by mixing gaseous fuel with combustion air is jetted from a nozzle port 51 opened on the inner peripheral surface of a cylindrical combustion chamber 3 in the tangential direction along the inner peripheral surface. The combustion chamber 3 is arranged in a storage area 7 of heating medium water 71. The peripheral surface 32 of the combustion chamber 3 is formed with a heat transfer wall in contact with the heating medium water 71. Flame formed by the premix gas 9 jetted from the nozzle port 51 is cooled to have low temperature by the heating medium water 71 through the heat transfer wall 32 so that NOx can be reduced.