A passenger weight measurement device for a vehicle seat which can be assembled to prevent the occurrence of the initial deformation and the initial load. The passenger weight measurement device 1 comprising a pair of left and right fixed lower rails 3 fixed on the floor of a vehicle, a pair of movable upper rails 4 disposed to be movable in a front-and-rear direction on each of the fixed lower rails 3, load sensors 50 and 60 fixed on an upper surface of the left movable upper rail 4, load sensors 70 and 80 mounted on the movable upper rail 4 to be movable in a left-and-right direction with respect to the right movable upper rail 4, and a rectangular frame 110 mounted on the load sensors 50, 60, 70, and 80.