A sensor apparatus includes a first capacitance element, a second capacitance element, a ground circuit, and a signal processing circuit. The first capacitance element has a first capacitance. The second capacitance element includes a first electrode and a second electrode that form a second capacitance larger than the first capacitance. The ground circuit includes a third electrode arranged adjacently to the first electrode, and converts the second capacitance into a third capacitance smaller than the second capacitance by connecting the third electrode to a ground potential. The signal processing circuit processes a first signal output from the first capacitance element based on a change of the first capacitance, and a second signal output from the second capacitance element based on a change of the third capacitance.