An internal combustion engine comprising: an intake port formed on a cylinder head configured to generate a swirl, a tumble and/or an inverse tumble in a cylinder; an exhaust port formed on the cylinder head; and a piston, wherein: the piston includes a top surface which is orthogonal to a central axis of the piston provided in an upper portion of the piston, a cavity that is axially symmetrical and centered around the central axis of the piston and is provided from the top surface toward a lower portion of the piston around the central axis of the piston, and a connection surface being a curved or a flat surface inclined with respect to the top surface and being disposed between the top surface and the cavity, while the connection surface is provided to be closer to a lower portion side of the piston than the top surface; and an area of the connection surface projected on a plane parallel to the top surface is larger on an intake port side than on an exhaust port side wherein when the piston is divided into two with one plane passing through the central axis of the piston the intake port side refers to the side that includes the intake port and the exhaust port side refers to the side that includes the exhaust port, characterized in that the connection surface is connecting an inner edge of the top surface and an upper end of a side surface of the cavity to each other; a central axis of a boundary line between the connection surface and the top surface has a circular or an elliptical shape and is eccentric to the intake port side with respect to the central axis of the piston; and a bottom surface of the cavity is parallel to the top surface. an intake port formed on a cylinder head configured to generate a swirl, a tumble and/or an inverse tumble in a cylinder; an exhaust port formed on the cylinder head; and a piston, wherein: the piston includes a top surface which is orthogonal to a central axis of the piston provided in an upper portion of the piston, a cavity that is axially symmetrical and centered around the central axis of the piston and is provided from the top surface toward a lower portion of the piston around the central axis of the piston, and a connection surface being a curved or a flat surface inclined with respect to the top surface and being disposed between the top surface and the cavity, while the connection surface is provided to be closer to a lower portion side of the piston than the top surface; and an area of the connection surface projected on a plane parallel to the top surface is larger on an intake port side than on an exhaust port side wherein when the piston is divided into two with one plane passing through the central axis of the piston the intake port side refers to the side that includes the intake port and the exhaust port side refers to the side that includes the exhaust port, characterized in that the connection surface is connecting an inner edge of the top surface and an upper end of a side surface of the cavity to each other; a central axis of a boundary line between the connection surface and the top surface has a circular or an elliptical shape and is eccentric to the intake port side with respect to the central axis of the piston; and a bottom surface of the cavity is parallel to the top surface. the piston includes a top surface which is orthogonal to a central axis of the piston provided in an upper portion of the piston, a cavity that is axially symmetrical and centered around the central axis of the piston and is provided from the top surface toward a lower portion of the piston around the central axis of the piston, and a connection surface being a curved or a flat surface inclined with respect to the top surface and being disposed between the top surface and the cavity, while the connection surface is provided to be closer to a lower portion side of the piston than the top surface; and an area of the connection surface projected on a plane parallel to the top surface is larger on an intake port side than on an exhaust port side wherein when the piston is divided into two with one plane passing through the central axis of the piston the intake port side refers to the side that includes the intake port and the exhaust port side refers to the side that includes the exhaust port, characterized in that the connection surface is connecting an inner edge of the top surface and an upper end of a side surface of the cavity to each other; a central axis of a boundary line between the connection surface and the top surface has a circular or an elliptical shape and is eccentric to the intake port side with respect to the central axis of the piston; and a bottom surface of the cavity is parallel to the top surface.