A light beam deflector includes an optical waveguide made of a material capable of propagating surface elastic waves therethrough, and n (n.gtoreq.2) surface elastic wave generating means for generating in the optical waveguide surface elastic waves which travel across the path of a guided wave traveling in the optical wave guide, thereby diffracting and deflecting the guided wave n times and amplifying the deflection of the guided wave caused by the diffraction thereof. Each of the n surface elastic wave generating means comprises an interdigital transducer having electrode fingers spaced at distances that vary stepwise, and a driver for applying an alternating voltage having a continuously varying high frequency to the interdigital transducer. The drivers apply alternating voltages having frequencies shifted from each other to the interdigital transducers, respectively, so that periodic variations in the intensities of the surface elastic waves generated respectively from the interdigital transducers will not amplify each other.