The present disclosure provides a variable compression ratio device including a piston, a piston pin, an eccentric cam, a connecting rod, a crank pin, a hydraulic pump, an oil jet injection nozzle, an oil jet control valve, and a control unit. In addition, a groove formed in a rotating direction of the eccentric cam is divided into a first chamber and a second chamber. The piston pin receives a hydraulic pressure through a path formed inside the crank pin and the connecting rod and receives the oil injected from the oil jet injection nozzle to control the hydraulic pressure supplied to the first chamber and the second chamber of the eccentric cam, thereby controlling the rotation position of the eccentric cam.