An auto-focusing device includes a light emitting element for emitting an optical beam to be projected upon an object, an image position detecting element for receiving the optical beam reflected from the object for outputting an image position signal, and range computing circuitry for receiving the image position signal and computing therefrom the range to the object and outputting a corresponding range signal. First and second level deciding circuits decide whether or not the computed data based on the image position signal is at a level validating the computation of the range signal. The level deciding circuits output a remotest or nearer-than-remotest signal dependent upon the computed image position signal if the computed data from the image position signal is not validated. A lens position setting device sets a lens position from either the range signal, the remotest signal or the nearer-than-remotest signal in accordance with the decisions of the first and second level deciding circuits.