A first processing circuit determines a collision of a vehicle based on an output from a sensor for detecting a collision of the vehicle. A second processing circuit outputs a signal to deploy an airbag based on an output from the first processing circuit. A communication unit controls information communication between the first processing circuit and an electronic control unit outside the airbag system. A first power supply unit generates a first driving voltage for driving the first and second processing circuits based on a voltage of an outside power supply. The first power supply unit includes backup power supply unit that supplies a backup voltage when the voltage of the outside power supply falls. A second power supply unit supplies a second driving voltage to the communication unit based on an output of the first power supply unit. A power supply control unit stops the supply of the second driving voltage from the second power supply unit to the communication unit on detection of a fall in the voltage of the outside power supply.