The underdrawing is a guideline for the artist to make the subject of painting. It can be only sketched or very fine, rich of details and shading, sometimes even using "chiaroscuro". Therefore, the underdrawing becomes an artwork itself, evidence of the artist's creative process, destined to remain hidden forever, but in some cases, again visible using the imaging technique known as infrared reflectography. The research group of the Archaeometry Laboratory, at Department of Physics and Earth Science of University of Ferrara, studies the pictorial artworks through a non-invasive approach. To this purpose an image diagnostics protocol has been defined also using instruments and devices specifically designed and developed. This work is focused on the development of a scanning device for wide band IR reflectography.