Occupant load sensor for a vehicle seat with flexible printed circuitry

An occupant load sensor of a seat for a vehicle includes a strain member, a connecting member, first and second strain gauge plates, an upper bracket, an amplifier substrate, and an FPC substrate. The strain gauge plates are attached to a surface of the strain member and respectively arranged between a central portion and both end portions of the strain member. Each strain gauge plate includes two strain detecting elements forming a half bridge circuit of a Wheatstone bridge circuit. The FPC substrate is connected to the amplifier substrate and to the strain gauge plates between the both end portions and the central portion of the strain member. Further, the FPC substrate includes a plurality of wiring patterns. The Wheatstone bridge circuit is formed with the plurality of wiring patterns and the half bridge circuit formed at each strain gauge plates.