an input device includes : a memory configured to store a length of a finger ; and a processor configured to obtain a depth image that includes a hand and has pixel values corresponding to a distance from a camera to subjects including the hand , detect a hand area that corresponds to the hand from among the subjects , from the depth image , identify a tip end of the hand area and a base of the finger , identify a first three - dimensional position that corresponds to the tip end and a second three - dimensional position that corresponds to the base , based on the pixel values of the depth image , identify a direction from the second three - dimensional position to the first three - dimensional position , calculate a third three - dimensional position that corresponds to a fingertip of the finger based on the direction and the length , and generate an input signal according to the third three - dimensional position .