Abstract: The device makes it possible to count series of products that are not very thick, stacked side by side, in a determined direction in a retention mechanism. The device includes a lighting mechanism producing one or more light beams covering the whole length of the stack, a detection mechanism with photosensitive elements and including an optical device, making it possible to focus light rays reflected by the stack, a processing mechanism receiving signals originating from the detection circuit, extracting light levels from these signals in correlation with a dimension of stack thickness expressed in pixels, and computing the number of products by determining the repetition of a pattern representative of a product in a noise-free signal resulting from a conversion of the signals received. A Fourier transform is respectively applied to correlation and bicorrelation functions of the signal in order to find a periodic pattern representative of a product if necessary to the nearest phase shift.