1. A method of controlling a contactless user-interface (UI) motion recognizing device, the method comprising: obtaining a left-eye image and a right-eye image; determining an object position of an object in the obtained left-eye image and the obtained right-eye image; determining an object brightness of the object; determining depth information of the object using the determined object brightness; determining a three-dimensional (3D) object position of the object using the determined object position and the determined depth information; determining an object moving velocity based on the determined 3D object position and a previous 3D object position; and determining a UI pattern based on the determined 3D object position and the determined object moving velocity, and executing an operation according to the determined UI pattern.