Abstract: A swirl chamber type combustion chamber for an internal-combustion engine is divided into a main combustion chamber and a swirl chamber connected through a passageway with the main combustion chamber. The main combustion chamber includes a clearance part defined between a cylinder head and a piston of the engine, a concavity or piston chamber provided in the upper surface of the piston, and an air reservoir.The air reservoir is preferably provided in portions of the piston upper surface where the concavity of the main combustion chamber is not present. It is preferable, but not essential, that the air reservoir have a suitable number of holes with a diameter-deepness ratio of 1 to 4 arranged symmetrically with respect to the concavity so that a line connecting the centers of the piston and each hole makes an angle of substantially 30.degree. to 120.degree. with a longitudinal center line of the concavity.