PURPOSE: To increase the sensitivity by a method wherein a pair of facing glanges are coupled to each other by a tube, a wire strain gauge is bonded within the tube, and changes in resistance due to strains in the wire strain gauge are detected.

CONSTITUTION: A pair of facing flanges 1, 1' are attached to a circular tube 4 by means of nuts 2 and bolts 3, respectively. A wire strain gauge is bonded within the tube 4 and resin 5 is filled up into an open space of the tube 4. Changes in resistance due to strains in the wire strain gauge are transmitted to a lead wire 7 and then to an electrometer. A strain guage with high sensitivity can be obtained by reducing the ratio of A2/A1 (A2 is sectional area of a member to which the wire strain gauge is bonded, A1 is sectional area of the flange) and also by properly selecting an elastic modulus of the member to which the wire strain gauge is bonded.