The present invention relates to an opening/closing device including a fixed plate, a moving plate that can be moved relative to the fixed plate, a slide plate that is formed having a slide groove, a hinge arm including a first shaft part rotatably connected to the fixed plate, a third shaft part rotatably connected to the moving plate, and a second shaft part provided between the first shaft part and the third shaft part, and configured to move the moving plate between a closed position and an open position relative to the fixed plate by centrally rotating about the first shaft part, a slide arm including a fourth shaft part rotatably connected to the moving plate and a fifth shaft part connected slidably along the slide groove of the slide plate, and configured to move the moving plate between the closed position and the open position relative to the fixed plate by rotating about the fourth shaft part, a link arm having one end part connected to the second shaft part and another end part connected to the fifth shaft part. The fifth shaft part is configured to slide inside the slide groove as the link arm moves along with the moving of the hinge arm when the moving plate is moved between the closed position and the open position. The moving plate and the fixed plate are positioned substantially on the same plane when the moving plate is moved to the open position.