A sensor apparatus for detecting a positional relationship includes a first electrode, an applying unit applying a charging signal with a first cycle period to the first electrode, a second electrode, a selecting unit selecting the first or second cycle period which have overlapped segment periods, an output unit outputting electrical signals supplied from the second electrode with the first cycle period, if the first cycle period is selected, and parts of the electrical signals during the segment periods, if the second cycle period is selected, a comparator comparing an amplitude of the electrical signals with a threshold value and generating a first or second comparison signal and a controller generating a proximity and non-proximity signal in response to the first and second comparison signal, respectively, so that the selecting unit selects the first and second cycle period in response to the proximity and non-proximity signal, respectively.