PURPOSE: To prevent ceramics of a piston head made of ceramics by providing a metallic ring between the ceramics and the main body of the piston.

CONSTITUTION: A piston main body 2 is made of aluminium alloy and provided with a skirt part 3. A piston head 7 is made of ceramic materials of silicon nitride and shaped to keep a combustion hollow 8 in the center of its upper face and a projection 9 on the lower side with an annular groove 10 around. A ring 11 made of number is fitted to the annular groove 10 of the piston head 7 by its inner projected part 12, and fixed between the piston main body 2 and the piston head 7 with its periphery 13 fitted to a concave inner wall 14 of the piston main body 2. Consequently, since the strong fastening force given to the ring 11 in a cooled state after a shrinkage fit is received by the rigidity of the ring 11 and not increased greatly, ceramic materials of the head 7 are prevented from cracking.