To enable not only a compression ratio but also an amount of exhaust gas to be changed in a compression ratio variable engine having: a connecting rod coupled to a piston; a first arm rotatably coupled to the rod and coupled to the crank pin of a crankshaft; a second arm coupled integrally with the first arm; a control rod rotatably coupled to the second arm; and a supporting shaft rotatably supporting the other end of the control rod and displaceable.

The amount Vhpiv0 of exhaust gas and the compression ratio piv0 when the supporting shaft 61 is disposed at an arbitrary first position and the amount Vhpiv1 of the exhaust gas and the compression ratio piv1 when the shaft 61 is displaced from the first position are obtained. In the case of piv1<piv0, the relation of Vhpiv1>Vhpiv0, and in the case of piv1>piv0, the relation of Vhpiv1<Vhpiv0 are set satisfied.