A beam deflector and a three-dimensional (3D) display device including the beam deflector are provided. The beam deflector includes a first deflector configured to controllably deflect incident light having a first polarization state in a first horizontal direction; a half-wave plate configured to rotate a polarization of light transmitted by the first deflector by 90°; and a second deflector configured to controllably deflect light transmitted by the half-wave plate having the first polarization state in a second horizontal direction that is different from the first horizontal direction.