Variable compression ratio engine

The invention provides a variable compression ratio engine that has a simple structure, easily ensures the sealability, and provides high reliability. In a variable compression ratio engine, a connecting rod 13 converts vertical movement of a piston 6 in a cylinder 5 into rotary movement of a crankshaft 14. The connecting rod 13 is divided into at least two portions. A control rod 21 is connected to or near a dividing section of the connecting rod 13. A support shaft position of the control rod 21 is displaced. The control rod 21 is coupled to a right cylinder rod 28 of a piston-type, both rod type, double-acting hydraulic cylinder 27. A piston section 35 of the hydraulic cylinder 27 is configured to freely move in accordance with displacement of the support shaft position of the control rod 21. A channel is used to connect two hydraulic chambers 43 and 44 divided by the piston section 35. The channel is configured to selectively permit supplying and stop supplying a working fluid from the right hydraulic chamber 43 to the left hydraulic chamber 44, and vice versa.