Disclosed herein are an X-ray input apparatus capable of exactly reflecting an operator's intention to perform calibration control, an X-ray imaging apparatus including the X-ray input apparatus, and a method of controlling the X-ray input apparatus. In accordance with an aspect of the present disclosure, an X-ray input apparatus comprises a body configured to be accommodated in a holder of an X-ray imaging apparatus. The apparatus also includes a touch sensor disposed on an outer circumferential surface of the body and configured to sense a touch. The apparatus also includes a radiation button disposed on a top of the body and configured to receive a control command from an operator. The apparatus also includes an input controller configured to perform calibration control when the body is accommodated in the holder, thereby deciding a capacitance threshold value of the touch sensor.