A sensor device includes a communication line having a high-level line and a low-level line, and printed wiring layers. The printed wiring layers are connected to the communication line so as to have a differential communication with an electronic control unit of an occupant protection system. First and second layers are ungrounded, and have a low-level conduction pattern connected to the low-level line and a circuit element having a standard corresponding to the low-level line. Third printed wiring layer is arranged between the first and second layers through insulations, and has a high-level conduction pattern connected to the high-level line.