A display device using a light modulator and having an improved numerical aperture (NA) of an after-edge lens system is disclosed. The display device includes an illumination lens, a diffractive light modulator, an NA improvement unit, a filter system and a projection system. The illumination lens converts light into linear parallel light, and outputs the linear parallel light. The diffractive light modulator produces diffracted light beams having a plurality of diffraction orders by modulating the linear parallel light incident from the illumination lens according to an external control signal. The NA improvement unit causes + and − diffracted light beams of the diffracted light beams to come close to each other. The filter system passes only some of the diffracted light beams having predetermined orders, therethrough. The projection system focuses the diffracted light beams onto an object and allows the focused diffracted light to scan the object.