A securing device for a tablet device has a main seat, two positioning rods, two first resilient elements, two driving sliders, two sets of holding legs and a lock. The holding legs hold the tablet device. When the lock is locked, the lock is unable to detach from the main seat, and the positioning rods, the driving sliders and the holding legs are unable to move. Consequently, the securing device is unable to detach from the tablet device. Thus, as a cable of the lock is looped around a post, the tablet device is secured at a specific position and is not stolen easily.