To provide a combustion device capable of carrying out the complete combustion of high-blending hydration fuel, and the reduction of fuel consumption.

Front and rear parts of a cylinder are formed into circular cones, a shell 4 is composed of steel, and its interior is composed of heat resisting steel. A fuel spraying burner 9 is installed at a rear circular cone end. One or several flame jetting tubes 6 are provided in a front circular cone end, the tip of each flame jetting tube 6 is enlarged larger than an inner diameter of the cylinder, and a jetting angle of high heat gas is enlarged. After the interior of a combustion device is heated to 700C or higher by spraying heavy oil or kerosene by the fuel spraying burner 9, the hydration fuel is sprayed and burned, and a spraying amount of heavy oil or kerosene is reduced. Fuel efficiency can be improved by spraying the high heat gas in a wide range in a combustion furnace by the several flame jetting tubes provided at the front circular cone end.