A sensor device includes a sensor circuit for measuring a physical amount such as pressure, a voltage detector for detecting a voltage actually supplied to the sensor circuit, and an oscillator for generating an oscillating signal when the voltage detector finds the voltage supplied to the sensor circuit is abnormally low. The sensor signal and the oscillating signal are selectively supplied to a controller. The controller controls various devices connected thereto based on the sensor signal, while it detects a malfunction of the sensor device based on either a high level signal or a low level signal in the oscillating signal. Thus, the malfunction of the sensor device is automatically detected without fail.