To provide an internal combustion engine of high efficiency.

In a closed interval continuous combustion type internal combustion engine, an intake pump 3 and a rotary engine 8 are disposed, a power transmission device 7 is disposed on a rotating shaft 2 between the intake pump 3 and the rotary engine 8, a combustion chamber 4 is disposed in a closed interval gas moving part between the intake pump 3 and the rotary engine 8, and a fuel injection port 5 and an ignition device 6 are disposed in the combustion chamber 4. When the internal combustion engine is started by external power, air is supplied to the combustion chamber 4 and compressed by the intake pump 3 so that the fuel is injected to the combustion chamber 4 from the fuel injection port 5, then the combustion is performed by the ignition device 6, and the rotary engine 8 is rotated by its thermal expansion, thus the power can be obtained.