A device for automatic battery-operated lighting of the inside of a piece of furniture comprises a body provided with fixing means on a surface of the furniture by means of a mounting surface thereof and a chamber containing an electric battery and a light source and from which the control end of a normally closed pushbutton contact protrudes frontally for the connection of the battery to the light source when the furniture is opened. The fixing means comprises a tongue, intended for resting at a corner of the surface of the furniture and a tooth facing the tongue that is intended to be inserted into a hole on set surface of the furniture. A hooking lever is rotatable on the base body from an unhooking position to a hooking position, controlling the movement of means for moving the tooth towards the tongue to cause the tooth to engage in the wall of the hole with a reaction on the tongue resting on the corner of the furniture.