The invention relates to the technical field of electricity saving, and discloses an energy-saving device capable of automatically recognizing whether or not people exist in an elevator and turning on an illuminating lamp. The energy-saving device comprises a shell, the elevator is movably connected in the shell, the left end of the elevator is movably connected to an extension spring, the lower end of the elevator is fixedly connected to a supporting rod, the lower end of the supporting rod is movably connected to a connecting rod, the lower end of the connecting rod is movably connected to a guide column, and the left end of the guide column is fixedly connected to a guide block. When the guide block moves leftwards, a leftward pushing force is applied to the guide block, so that the interior is compressed, elastic potential energy is gathered in the guide block, preparation is made for resetting of the guide block, meanwhile, when the guide block moves leftwards, a leftward pushing force is applied to the contact, so that the contact is pushed to move leftwards to make contact with a trigger mechanism, and an internal circuit is connected, therefore, the effects that only when people exist in the elevator, the internal lamp is lightened, and when nobody exists, the internal bulb is turned off are achieved.