PURPOSE: To obtain a stable measurement without throwing-off the zero balance regardless of overload applied, by setting the value of radius of holes composing a thin deformable part at less than a specified value.

CONSTITUTION: A beam body 1, holes 3 and 4, thin deformable parts 5W8, a strain gauge 12 and the like are provided. The radius R of the holes 3 and 4 composing the thin deformable parts 5W8 is set at less than a specified value to minimize the permanent strain when the overload is applied. The length L of the strain gauge 12 along the length of the beam 1 is set corresponding to the radius R. Thus, stable measurement can be done without breaking zero balance with limited permanent deformation of the beam body 1 even when an overload is applied.