An internal combustion engine comprises a first raised portion formed on the inner wall of the cylinder head, a second raised portion formed on the top face of the piston at a position opposite to the first raised portion with respect to the axis of the piston, and a third raised portion formed on the inner wall of the cylinder head above the second raised portion. A first flat squish area is formed between the flat peripheral top face of the piston and the flat bottom face of the first raised portion. A second spherical shell shape squish area is formed between the spherical bottom wall of the third raised portion and the spherical rear face of the second raised portion. The third raised portion has a steeply inclined side wall extending upwards from the ridge of the second raised portion. A depression having a vertically extending peripheral wall is formed in the central portion of the top face of the piston. The peripheral wall is aligned with the vertically extending side wall of the first raised portion.