A first control signal generating unit and a second control signal generating unit output a first control signal and a second control signal when magnitude of an impact corresponding to first and second sensor signals are greater than a first and second threshold. A third control signal generating unit outputs a third control signal when detecting disruption of the second sensor signal. An activating signal generating unit activates a protecting device when the first control signal is output, and when one of the second control signal and the third control signal is output. A fourth control signal generating unit outputs a fourth control signal when detecting an abnormality other than disruption of the second sensor signal. The third control signal generating unit restricts outputting the third control signal when the fourth control signal is output.