A sleeping device is installed in a notebook computer with a mainframe and a flat panel display. The sleeping device includes a tab, an opening, a printed circuit board and a resilient metal. The tab is secured to the flat panel display. The opening is formed on an upper plate of the mainframe. The printed circuit board is disposed on a lower plate of the mainframe. Two conductive coatings are disposed on the printed circuit board. The resilient metal is disposed between the upper plate and the printed circuit board. The resilient metal is secured on the upper plate at one end to suspend an opposite end. When the flat panel display folds against the mainframe, the tab passes through the opening to press the resilient metal down such that the contact sections are in contact with two conductive coatings to enable the notebook computer to enter a sleeping mode.