VARIABLE-COMPRESSION-RATIO INTERNAL COMBUSTION ENGINE

An upper oil pan assembly (25) is attached to the lower portion of a cylinder block (12). An opening (33) is formed on a side wall (31) of the upper oil pan assembly (25). The variable compression ratio mechanism changes a top dead center position of a piston in accordance with the rotational position of a control shaft to thereby change the compression ratio. The control shaft is rotationally driven by an actuator (30). At least a portion of the actuator (30) is fixed to a main bearing cap (13) in a state in which at least a portion thereof is positioned on the outer side of an upper oil pan assembly (25).