PURPOSE: To improve the strength of a boundary part, to alleviate notch sensitivity and to prevent the occurrence of cracks by screwing a load cell having a built-in strain gage into load shell, and thereafter performing plastic deformation for the peripheral part of the boundary part.

CONSTITUTION: When a load cell 2 is mounted in a load shell (tubular body) 1 by screwing, the load cell 2 is set so that the cell 2 is made to protrude slightly higher than the surface of the shell 1. For example, the strong force is applied on the peripheral part of a boundary part with a punch, a hammer or the like, and a plastic deformation part 11 is formed so as to form a unitary body physically for a gap C together with a surface layer part. Thus, the strength of the boundary part is strikingly improved, notch sensitivity is alleviated and the occurrence of cracks in a coating 6 is prevented.