The E-pretensioner unit operates the motor-driving controls based on F-CAN data it receives from the adaptive cruise control unit, VSA modulator-control unit, and the ECM/PCM. Also the E-pretensioner unit receives seat belt buckle switch signals from the SRS unit by an interactive communication function. The E-pretensioner unit has a self-diagnostic function, and if it detects a malfunction, it sends its information to the SRS unit. The SRS indicator is then turned on by the SRS unit.