A projection device that continuously projects the free interior cross section of a tunnel to be excavated, in which the projector device (11) comprises: a measuring device (12) that acquires data on distances from the physical location of the actual measuring device to the surface where excavation of the transverse section of the tunnel is taking place; an orienting device that geographically positions the measuring device in accordance with a predetermined topographic reference system; and a projector laser (13) that provides a laser beam corresponding to the transverse section of the tunnel to be excavated, supplied from a controller module.
