PURPOSE: To reduce the burning noise during the drive of an engine by providing the first ignition plug to face to a combustion chamber and the second ignition plug to face to a squish zone for operating the second ignition plug only at the time of high-speed revolution and high load.

CONSTITUTION: A cylinder head 5 is fitted on the upper face of a cylinder block 1 to be provided with a partial concave part 4 on which an air inlet port is opened, and a combustion chamber 7 is formed by the concave part 4. A squish zone 8 is formed between the internal wall of the cylinder head 5 excluding the concave part 4 and a piston upper face 3a, and an exhaust port 11 is opened on the internal wall of the cylinder head 5 facing to this zone 8. In the engine with the above-said construction, the first ignition plug 13 to face to the combustion chamber 7 on the cylinder head 5 and the second ignition plug 15 to face to the squish zone 8 in a small concave part 14 shaped on the cylinder head 5 are arranged for the igniting work respectively at the time of normal, high-speed, and high-load operations.