A variable compression ratio device that includes a piston, a piston pin, and a connecting rod of which one end is connected to the piston by the piston pin, may include an eccentric ring rotatably coupled in a ring at the one end of the connecting rod, wherein the inner circumference thereof rotatably contacts with the outer circumference of the piston pin, an operating pin that longitudinally reciprocates in the piston pin, variable sliders that selectively contact one of both ends of the operating pin under a cylinder to push the one of both ends to the opposite side, and a guide plate that slidably supports the variable sliders, wherein, one end of a variable shaft selectively rotating is connected to the variable slider and a sliding direction of the variable slider is controlled by the rotation of the variable shaft.