In a vehicle seat, a central support member typically consisting of wire mesh or grid and supports most of the load of the vehicle occupant via spring members, and undergoes a relatively large displacement when the occupant is seated in the seat. Thus, by detecting the displacements of various parts of the central support member, preferably peripheral parts thereof, the magnitude of the total load and distribution of the load can be evaluated both reliably and accurately. Additionally, displacement sensors for measuring such large displacements are relatively inexpensive and easy to handle. Also, such sensors would not interfere with the existing seat designs, and would not be adversely affected by the equipment of the seat such as seat heaters.