Abstract: A reentrant combustion chamber is disclosed. The reentrant combustion chamber includes a profile forming the inlet of the combustion chamber that is a projective surface formed inward in the combustion chamber and the bottom of the combustion chamber that is a recessed space that is recessed outward under the inlet in the combustion chamber, a cone formed in a truncated cone shape continuing from the profile and protruding to the central space in the combustion chamber, and a top end for expanding the space of the combustion chamber by expanding the top of the combustion chamber at the inlet of the combustion chamber.