A light from a laser light source (11) is collected at a position of a slit (125a) in a vertical direction by a first optical system (12a) to form an intermediate image which is long in a horizontal direction corresponding to an arrangement direction of light modulator elements. An undesired light such as side lobes which appear on the both sides of the intermediate image in the vertical direction is blocked by a slit (125a) and the intermediate image is reformed by a second optical system (12b), to direct a liner illumination light onto the spatial light modulator (13). Thus, in a state where moving ribbons are sagged and first order diffracted lights are emitted in a light modulator element, it is possible to prevent a zeroth order light from being emitted from both end portions of ribbons, to thereby enhance contrast of the signal light.