An occupant load sensor of a seat for a vehicle includes a metal-made bracket fixed to a strain member and having an attachment portion extending in a lateral direction from the strain member, an amplifier substrate for amplifying a signal transmitted by the strain gauge. One surface of the amplifier substrate is covered by the attachment portion of the metal-made bracket and the other surface thereof is covered by a metal-foil ground pattern. The occupant load sensor further includes a resin-made amplifier case fixed to the attachment portion of the metal-made bracket and arranged in parallel to the strain member. The resin-made amplifier case houses therein the amplifier substrate.