A noise processing apparatus measures a first potential difference signal, between a first electrode and a second electrode that is used as a reference electrode, and measures a second potential difference signal, between the second electrode and a third electrode that is arranged on the steering unit in the apparatus. The apparatus calculates the difference between the intensities of the first potential difference signal and the second potential difference signal calculated at the predetermined intervals. The apparatus corrects the first potential difference signal or the second potential difference signal by using the calculated difference such that the intensities of the first potential difference signal and the second potential difference signal are canceled out. The apparatus calculates a differential signal indicating the difference between the first potential difference signal and the second potential difference signal by using the corrected potential difference signal, and outputs the differential signal.