A load detection device for a vehicle seat mounted between a floor side mounting mechanism made of metal and a seat side mounting mechanism made of metal and measuring a load applied by an occupant seated on the vehicle seat includes a strain generating body adapted to be fixed via both end portions to a fitting surface formed at one of the floor side mounting mechanism and the seat side mounting mechanism while having a predetermined clearance from the fitting surface, a strain gauge attached to the strain generating body, a bracket made of metal and including an attachment portion that extends laterally relative to the strain generating body, and an amplifier substrate mounted on the attachment portion while being arranged in parallel to the strain generating body, both surfaces of the amplifier substrate being covered by one of or more of the bracket, the floor side mounting mechanism and the seat side mounting mechanism, the amplifier substrate amplifying a signal output from the strain gauge.