A fluid system 10 according to the present disclosure includes an EAP sensor 13 disposed on an outer surface of a circuit conduit 11. The EAP sensor 13 includes a polymer element 131 including electrode layers 133A, 133B provided at respective surfaces of an ion-conductive polymer layer 132. The EAP sensor 13 is configured to output a signal corresponding to a deformation of the circuit conduit 11.