An internal combustion engine including at least one engine cylinder includes a cylinder cavity with first and second stopping members interconnected by a cylinder wall, the cylinder further includes two piston members slidably moveable within said cylinder cavity and between extreme positions intermediate between two stopping members, two piston members combust between their faces and cylinder wall pushing them with their power transmittal members alternatively to revolve the cogwheel and axle. By the ratchet function of power transmittal member or cogwheel, each piston has its free returning movement without clinging with the cogwheel and axle, allowing each piston continuously and alternatively revolves the axle without waste of energy for returning movements. An internal combustion engine having the free return movement by this invention has different choices of engine making in one or two pistons, one fuel or two fuels, stopping members or no stopping members for different engine requirements, substantially increases the usable engine power to enhance efficiency and reduces the weight to power ratio.