An object of the present invention is to provide a sensor device which is used in the state of being bonded to a living body, thereby making it possible to trace a deformation of a surface of the living body easily and further attain the tracing surely. The sensor device includes a sensor element. The sensor element includes a sheet-like first dielectric layer including an elastomer composition and a first electrode layer and a second electrode layer each including an electro-conductive composition containing carbon nanotubes. The first and the second electrode layers are formed on a top surface and a bottom surface of the first dielectric layer respectively, and are at least partially opposed to each other across the first dielectric layer. The at least partially opposed portions of the first and the second electrode layers constitute a detection portion, and the sensor element is reversibly deformable to change in an area of the top surface and the bottom surface of the first dielectric layer. The sensor device includes the measurement instrument for measuring a change in a capacitance of the detection portion. The sensor device is used in the state of being bonded to a living body and is utilized to trace a deformation of a surface of the living body.