An attachment structure for installing a load sensor to a vehicle seat includes the load sensor having a plate-shaped strain unit and a strain gauge for detecting a strain of the plate-shaped strain unit. The load sensor is structured that one end of the plate-shaped strain unit is fixed to a seating portion of the vehicle seat and the other end of the strain unit is fixed to a vehicle body. Also, a strain portion is defined between each fixed end of the plate-shaped strain unit, and the strain portion is deformable in a vertical direction relative to the vehicle seat. In addition, a load input point from the seating portion is defined approximately at a central portion of the strain portion of the plate-shaped strain unit.