A sensor device for detecting a positional relationship between a first member and a second member, includes a first charge-holding electrode provided on a surface of the first member and holding a charge, a second charge-holding electrode provided on the surface of the first member and holding a charge differing from the charge held by the first charge-holding electrode, a first charge-induced electrode provided on a surface of the second member, the first charge-induced electrode having a charge induced therein in accordance with the charge held by the first charge-holding electrode, when the first charge-holding electrode approaches the first charge-induced electrode, a second charge-induced electrode provided on the surface of the second member, the second charge-induced electrode having a charge induced therein in accordance with the charge held by the second charge-holding electrode, when the second charge-holding electrode approaches the second charge-induced electrode.