The present invention relates to a scanning apparatus using a light modulator. The scanning apparatus simultaneously and horizontally scans a plurality of diffracted beams, formed by actuating cells turned on/off in response to externally applied drive power, onto a photosensitive member. The scanning apparatus includes a first lens unit for converting a single beam, emitted from a light source, into collimated light, and emitting the collimated light. A light modulation means includes a plurality of actuating cells turned on/off by drive power, and diffracts and modulates the single beam to form a plurality of diffracted beams by on/off operation of the actuating cells. A filtering means selectively allows diffracted beams having at least one predetermined diffraction coefficient, among the plurality of diffracted beams formed by the light modulation means, to pass therethrough. A second lens unit focuses the plurality of diffracted beams selectively passing through the filtering means onto a photosensitive member.