Weight detector for vehicle seat

A weight detector for detecting the weight of a passenger seated on a vehicle seat includes a first load sensor and a second load sensor provided on opposite sides of a rear portion of the vehicle seat. Each of the first and second load sensors has a predetermined detection range. The weight detector further includes a third load sensor and a fourth load sensor provided on opposite sides of a front portion of the vehicle seat. Each of the third and fourth load sensors has a predetermined detection range. If a detection value based on a load acquired by one of the first through fourth load sensors exceeds its detection range, the weight detector uses an old value that was determined under proper condition. Otherwise, the weight detector determines the size of the passenger based on the currently detected values.