A sensor unit includes a pressure sensor, an acceleration sensor and a signal-processing circuit, which are disposed on the bottom surface of a lead to form a line in the longitudinal direction of the sensor unit. The pressure sensor and the acceleration sensor are disposed at respective symmetrical positions with respect to the center of the signal-processing circuit in the longitudinal direction of the sensor unit. Each of the pressure sensor and the acceleration sensor has substantially the same height dimension. The sensors, the signal-processing circuit and the lead are sealed with a molded body, in such a manner as to allow lead terminals of the lead to protrude outside the molded body. The signal-processing circuit is operable, based on a signal from the acceleration sensor, to control the ON/OFF action of the pressure sensor.