Each acceleration sensor of an air bag system includes a sensing device, a communication device and an adjusting device. The sensing device generates a measurement signal, which indicates a measurement value of acceleration. The communication device performs two-way communication relative to a master ECU and each remaining one of the acceleration sensors of the air bag system. The adjusting device adjusts the measurement value based on a physical quantity application state of its own acceleration sensor and a physical quantity application state of each remaining one of the acceleration sensors.