Patent ID: 7419026

Claim:
A seat belt device comprising: a seat belt for constraining an occupant to a seat; tension varying means constructed and arranged for applying a tension to the seat belt, wherein the tension varying means is provided at a first part supporting the seat belt or a second part supporting the seat belt; tension detecting means for detecting an actual tension on the seat belt, wherein the tension detecting means is provided at the first part supporting the seat belt or the second part supporting the seat belt; and failure detecting means for comparing the tension applied by the tension varying means to the actual tension detected by the tension detecting means, to detect failures of at least one of the tension varying means and the tension detecting means when a difference between the tension applied by the tension varying means and the actual tension measured by the tension detecting means is greater than a predetermined value, wherein the predetermined value is selected as a value larger than a tension loss from the tension varying means to the tension detecting means.