A one-dimensional (1D) spatial light modulator (SLM) and an image output device employing the same are provided. The 1D SLM includes: a light deflector including a light guide that is formed of a photonic crystal material having a refractive index that can be varied according to an applied voltage and allows incident light to continue along an original propagation path or deflects the incident light from the original propagation path on a pixel-by-pixel basis, and an electrode portion individually applying a voltage to the light guide; and a light blocking member facing a light exiting surface of the light deflector and blocking a portion of light exiting the light deflector.