A sensor mechanism body (1; 51; 61), comprising: a main Roberval mechanism provided with a first fixed column fixed to or integrated with an electronic balance base, a first movable column for transmitting the load of an object to be measured placed on a weighing plate, and two first beams (12, 13) parallel to each other for connecting the first movable column to the first fixed column so that the first movable column transmits the load of the object to be measured in the vertical direction; a sub-Roberval mechanism provided with a second fixed column fixed to or integrated with said electronic balance base, a second movable column for transmitting the load of an internal weight mounted on an engaging section, and two second beams (22, 23) parallel to each other for connecting the second movable column to the second fixed column so that the second movable column transmits the load of the internal weight in the vertical direction; a first lever rockably supported by a first fulcrum where the first movable column in the main Roberval mechanism is connected to a first end and a second lever is connected to a second end; and the second lever rockably supported by a second fulcrum where the second movable column in the sub-Roberval mechanism is connected to one end, and an electromagnetic force generating device and the second end of the first lever are connected to the other end, wherein said main Roberval mechanism, sub-Roberval mechanism, first lever and second lever are formed so as to be integrated into a rectangular parallelepiped block through a number of through holes and slits provided so as to penetrate in the direction of the thickness, which is perpendicular to said vertical direction, characterized in that the second fixed column in said sub-Roberval mechanism is connected to the second lever through a thin-walled connection section where cuts (43a, 43b; 52a, 52b; 62c, 62d, 63c, 63d) are created in opposite ends in the direction of the thickness. a main Roberval mechanism provided with a first fixed column fixed to or integrated with an electronic balance base, a first movable column for transmitting the load of an object to be measured placed on a weighing plate, and two first beams (12, 13) parallel to each other for connecting the first movable column to the first fixed column so that the first movable column transmits the load of the object to be measured in the vertical direction; a sub-Roberval mechanism provided with a second fixed column fixed to or integrated with said electronic balance base, a second movable column for transmitting the load of an internal weight mounted on an engaging section, and two second beams (22, 23) parallel to each other for connecting the second movable column to the second fixed column so that the second movable column transmits the load of the internal weight in the vertical direction; a first lever rockably supported by a first fulcrum where the first movable column in the main Roberval mechanism is connected to a first end and a second lever is connected to a second end; and the second lever rockably supported by a second fulcrum where the second movable column in the sub-Roberval mechanism is connected to one end, and an electromagnetic force generating device and the second end of the first lever are connected to the other end, wherein said main Roberval mechanism, sub-Roberval mechanism, first lever and second lever are formed so as to be integrated into a rectangular parallelepiped block through a number of through holes and slits provided so as to penetrate in the direction of the thickness, which is perpendicular to said vertical direction, characterized in that the second fixed column in said sub-Roberval mechanism is connected to the second lever through a thin-walled connection section where cuts (43a, 43b; 52a, 52b; 62c, 62d, 63c, 63d) are created in opposite ends in the direction of the thickness.