The invention provides an internal combustion engine and an engine. The internal combustion engine comprises a combustion chamber; cylinder holes are formed in the two opposite side walls of the combustion chamber respectively; a first piston and a second piston which are matched with cylinder holes are arranged in the cylinder holes respectively, and are controlled through a linking crank shaft to conduct relative motion; a compressible spring used for storing energy is arranged on the piston rod of the first piston; an igniting device and an air exchange device are arranged in the combustion chamber; the igniting device is arranged at the corresponding position of the maximal stroke of the second piston extending in the combustion chamber; the air exchange device is arranged at the corresponding position of the minimum stroke of the second piston extending in the combustion chamber. According to the invention, a cylinder cover structure is eliminated; a valve timing mechanism is innovated; component amount of the whole engine is greatly simplified; the cost is reduced; the mechanical efficiency of the engine is improved.