PURPOSE: To obtain the device which is capable of detecting a load correctly and is excellent in weatherproofness by bonding strain gages to the inside surface of the hole of a hollow-pipe-shaped beam, while intercepting the same from the outside air.

CONSTITUTION: A load point 1' is provided at the tip of the hollow-pipe-shaped beam 1, while the other end of the beam is set as a fixed end, and to the inside surface thereof are bonded the strain gages 2aW2d. Moreover, a gage cord 8 is led outside through the intermediary of airtight terminals 7 and thus the strain gages 2aW2d are intercepted from the outside air, while inactive gas 4, for instance, is enclosed to prevent the influence of moisture, etc. By this constitution, when the beam 1 is bent by application of the load in the direction of an arrow 3 to the load point 1', relatively large shear strain is generated in all the area of the lateral surface of the beam 1 and, therefore, even relatively small load can be detected correctly. In addition, since the device is fully airtight, it suffers little changes with years and is free from the influence of moisture.