A power plant includes an internal combustion engine having a crankshaft to which a piston is connected and a variable compression ratio system for changing the position of the axis of rotation of the crankshaft. The power plant includes a transmission having a main shaft which is connected to the crankshaft through a first deceleration system. The variable compression ratio system includes a crankshaft holder, which rotatably supports the crankshaft and which is swingably supported on a main shaft, and a drive system which swings the crankshaft holder. Thus, the power plant retains unchanged the distance of shafts between the crankshaft and the main shaft, even when the combustion engine has a variable compression ratio system, by changing the position of the axis of rotation of the crankshaft.