An embodiment of the invention provides an apparatus for measuring a conductive pattern on a substrate, which includes a first electro-optical modulator surrounding at least one first detecting roller; transmission rollers for transferring the substrate and allowing direct contact of the substrate and the first electro-optical modulator; a voltage supplier for providing a bias between the first electro-optical modulator and the substrate; and a first image detecting system for receiving a first detecting light reflected from a first surface of the substrate.