An internal combustion engine, comprising: a piston including a piston head section having first and second skirt portions and a pin boss portion, the piston reciprocating in a cylinder; a multi link piston-crank linking mechanism (4, 5, 10) linking the piston and the piston pin with a crankshaft, the multi link piston-crank linking mechanism including an upper link; a lower link and a control link; and the crankshaft including a counterweight having an outermost portion, wherein the upper link has a first end connected with the piston by the piston pin; the lower link has a first end connected with a second end of the upper link by a first connection pin, and is mounted rotatably on a crankpin of the crankshaft; and the control link has a first end connected with a second end of the lower link by a second connection pin and a second end supported movably relative to a body of the internal combustion engine, characterized in that the counterweight having the outermost portion crosses an imaginary extension line extended from the piston pin in an axial direction of the piston pin when the piston is located in proximity of a bottom dead center, such that the outermost portion of the counterweight passes a side of the pin boss portion of the piston and the piston pin without conflicting with the pin boss portion and each of the first and second skirt portions of the piston and the piston pin and the counterweight projects outwardly beyond the piston head portion of the piston in the axial direction of the piston pin, when the piston is located in proximity of the bottom dead center, wherein the upper link is positioned with a small inclination with respect to an axis of the cylinder when the piston is located at a position at which the piston undergoes a maximum combustion pressure. a piston including a piston head section having first and second skirt portions and a pin boss portion, the piston reciprocating in a cylinder; a multi link piston-crank linking mechanism (4, 5, 10) linking the piston and the piston pin with a crankshaft, the multi link piston-crank linking mechanism including an upper link; a lower link and a control link; and the crankshaft including a counterweight having an outermost portion, wherein the upper link has a first end connected with the piston by the piston pin; the lower link has a first end connected with a second end of the upper link by a first connection pin, and is mounted rotatably on a crankpin of the crankshaft; and the control link has a first end connected with a second end of the lower link by a second connection pin and a second end supported movably relative to a body of the internal combustion engine, characterized in that the counterweight having the outermost portion crosses an imaginary extension line extended from the piston pin in an axial direction of the piston pin when the piston is located in proximity of a bottom dead center, such that the outermost portion of the counterweight passes a side of the pin boss portion of the piston and the piston pin without conflicting with the pin boss portion and each of the first and second skirt portions of the piston and the piston pin and the counterweight projects outwardly beyond the piston head portion of the piston in the axial direction of the piston pin, when the piston is located in proximity of the bottom dead center, wherein the upper link is positioned with a small inclination with respect to an axis of the cylinder when the piston is located at a position at which the piston undergoes a maximum combustion pressure.