To improve heating efficiency; and to reduce generation quantity of nitrogen oxides NOx.

This sealed cookstove 4 is constituted by arranging a heating top plate 3 for placing and heating a heating object 2 such as a pan in an upper part of a casing 1. An air-fuel mixture injection nozzle 8 is arranged in a combustion chamber constituting material 6 for constituting a combustion chamber 7 under a heating part 5 for placing the heating object 2 of the heating top plate 3. The air-fuel mixture injection nozzle 8 is connected with a premixed air supply pipe 12 provided with a mixer 11. The mixer 11 is connected with an air supply pipe 15 provided with a fan 13 and an air flow regulating valve 14, and a fuel supply pipe 18 provided with a fuel control valve 16 and a fuel pressure regulating valve 17. The air flow regulating valve 14 and the fuel pressure regulating valve 17 are respectively adjusted so that a flow speed of the premixed air jetted from the air-fuel mixture injection nozzle 8 becomes 1.5 times or more of a combustion speed of the air-fuel mixture in the combustion chamber 7, and are constituted so as to be heated by a planar flame F by forming the planar flame F.