To provide an internal combustion engine capable of enhancing its combustion efficiency by promoting the growth of flame in a combustion chamber.

The combustion chamber 18 has a suction port 19 and an exhaust port 20 and a suction valve 21 and an exhaust valve 22 to open and close the ports, and an ignition plug 44 installed in the center of the ceiling of the chamber 18 while a cavity 14a is formed at the top face of a piston 14, and at the ceiling surface 18a of the chamber 18, a recess 61 extending only toward the exhaust port 20 from the ignition plug 44 is formed.