Internal-combustion engine

The invention relates to an internal-combustion engine which is designed for mainly solving the problems that a piston of a prior internal-combustion engine generates lateral stress for a cylinder wall when moving up and down, and the prior internal-combustion engine has low power. The internal-combustion engine provided by the invention comprises a lower box body, an upper box body, an air cylinder, a cylinder cover, a cam shaft, an air inlet cam, an exhaust cam, an air inlet valve, an exhaust valve, an oil injection nozzle or a spark plug, a straight-bar leading sleeve, a piston, a crank output shaft, a chain, a cam shaft chain wheel, a straight bar, a straight-bar shaft, a sliding lever and a lever fulcrum shaft. The invention has the advantages that when the piston moves up and down, the straight-bar shaft drives the sliding lever to push the crank output shaft to rotate so as not to generate lateral stress for the cylinder wall, thereby having high working power.