A sensor apparatus includes a first member, a second member, and a detection mechanism. The second member is relatively movable in a first direction with respect to the first member. The detection mechanism includes an elastic member arranged between the first member and the second member, a support that is provided between the first member and the elastic member and forms an air layer between the first member and the elastic member, the air layer having a thickness changed by an elastic deformation of the elastic member, and an electrode pair that forms a plurality of capacitances including a capacitance component changed in accordance with a change of the thickness of the air layer. The detection mechanism outputs a detection signal on a movement amount of the second member in the first direction based on a change of a combined capacitance of the electrode pair.