We propose an electro-optic mode deflection device based on an annealed proton exchange (APE) waveguide in lithium niobate, associated with isosceles-triangle-shaped array electrodes and a horn-shaped input waveguide. The input waveguide is tapered down to ensure that the output of the device has a good beam quality, i.e., a quasi-single mode in this case. This new device allows beam deflection at a relative low voltage and large deflection angle. At an APE-waveguide width of 80 μm, mode deflections of 0.265 and 0.240 μm/V are obtained for 1064 and 980 nm, respectively. This beam deflection device can be applied in high-speed optical switch, and beam smoothing of a high-power laser, etc.