A seat weight measuring apparatus includes a support body one end of which is fixed in position relative to a vehicle body and the other end of which is displaced corresponding to a load from a vehicle seat side. The apparatus includes a permanent magnet which is disposed at one end of the support body and a held body which has a shape retaining property and is held by the other end of the support body, and a detector which is disposed on a tip of the held body to face the permanent magnet with a space therebetween.