Piston for internal combustion engine

A piston of an internal combustion engine comprising:

• a combustion chamber that is formed at a piston top surface;
• and
• an oil gallery that is formed so as to surround the combustion chamber, wherein
• a wall thickness from a sliding side surface of the piston to the oil gallery is set greater on a piston skirt side than on a piston top surface side,
• wherein the oil gallery includes an outer surface and a curved bottom surface, the outer surface approaching a piston central axis in a cross section along the piston central axis, as the outer surface extends from the piston top surface side to the curved bottom surface on the piston skirt side, and
• wherein (B−A)/L≧0.05 is satisfied, in a cross section along the piston central axis, where a length of the oil gallery in an extending direction of the piston central axis is L, a lowest wall thickness from the sliding side surface to the piston top surface of the oil gallery is A, and a wall thickness from the sliding side surface to an intersection point W is B, where the intersection point W is a point of intersection between a virtual line V1 passing through a lower end of the oil gallery and orthogonal to the piston central axis and an extended line V2 extending along the outer surface immediately above the curved bottom surface.