An acousto-optic device capable of increasing a range of a diffraction angle of output light by using a nanostructured acousto-optic medium, and an optical scanner, an optical modulator, a two-dimensional/three-dimensional (2D/3D) conversion stereoscopic image display apparatus, and a holographic display apparatus using the acousto-optic device. The acousto-optic device may include a nanostructured acousto-optic medium formed by at least two different mediums repeatedly alternating with each other, wherein at least one of the at least two different mediums includes an acousto-optic medium. The acousto-optic device having the aforementioned structure may increase the range of a diffraction angle of output light. Thus, various systems such as the optical scanner, the optical modulator, the 2D/3D conversion stereoscopic image display apparatus, and the holographic display apparatus may not require a separate optical system to increase an operational angle range, thereby decreasing a size of the system and/or improving a resolution of the system.