To surely prevent the generation of knocking with a simple structure by providing an igniting means at different portions of the same combustion chamber of an internal combustion engine and changing an igniting position of the igniting means in the same combustion chamber at each cycle.

In a two-cylinder engine with ignition plugs, ignition plugs 3, 13 are fixed to the cylinder head 2 of one cylinder and are connected to a distributor 5 via a high tension cord 4. When the fuel-air mixture in a combustion chamber is ignited by the ignition plug 3 and a burning region A spreads from the left to the right to compress a region B unburned, a knocking N is generated in the region B unburned and increases temperatures rapidly and hence tends to produce a heat spot H there in the cylinder 1. Therefore, the ignition plug 13 is fixed to this spot H and ignites the fuel-air mixture in the next cycle to prevent an abnormal increase in temperature at the knocking spot, which prevents the knocking spot from being a heat spot.