In recent years, there is a tendency toward enforcing a safety of a passenger of a vehicle. In order to improve the safety of the passenger who sits on a seat, a restraint function of a seat belt and an operating function of an air bag in accordance with a weight of the passenger have been developed. When these devices are adopted, an accurate detection of a weight of the passenger is needed. As for one such means, a known device is disclosed in Japanese Patent Laid-Open Publication No.2001-12998. The known device applies a means for attaching a weight sensor (ie., an attachment structure of a load sensor) to a seat mounted in a vehicle (ie., a vehicle seat).
Normally, as for a weight sensor to detect a weight of the passenger who sits on a seat cushion of the vehicle seat, a sensor with a strain gauge disposed in a plate-shaped strain unit is used for detecting a vertical strain of the strain unit. Therefore, in order to detect the weight of the passenger on the seat accurately, a precise input of the weight from the seating portion to a strain portion of the strain unit is needed. Thus, an attachment structure of a load sensor for a vehicle seat is particularly important.
However, in the known device, such importance of the attachment structure of the load sensor to the vehicle has not been recognized, and is designed merely not to exceed a height of the seating portion in a normal sitting condition when the weight sensor is attached.