A seat weight measuring apparatus capable of securely withstanding large force due to large load, such as force in the event of a vehicle collision, applied to a vehicle seat. Normally, a small force is applied to a rear pin bracket and the sleeves through which a pivot bolt is inserted do not substantially collide with the inner peripheries of holes. As a large force is applied to the rear pin bracket, a stopper bolt collides with a base frame and the rear pin bracket collides with the pivot bolt. The large force exerted on the rear pin bracket is shared and borne by portions of the frame thereby reducing the localized stresses in the frame.