Four load sensors having an upper limit value in a detection range are mounted
in a seat of a vehicle. The weight of an occupant sitting on the seat is detected
as a total of outputs from the load sensors. When the detected weight of the occupant
is equal or larger than a predetermined value, the deployment of the air bag is
permitted, and when the detected weight of the occupant is smaller than the predetermined
value, the deployment of the air bag is prohibited. When any one of the outputs
from the plurality of load sensors is the upper limit value in the detection range,
the deployment of the air bag is permitted irrespective of the detected weight
of the occupant. Thus, even when the output from the load sensor has been modified
to the upper limit value by a limiting process, so that the weight of the occupant
is calculated as a value smaller than an actual weight to become smaller than the
predetermined value, the air bag can be deployed reliably to restrain the occupant.
