Building means, having a main plate 1, a flexible sheet 2 attached thereto, a first bolt portion 4 extending outwards of the plate 1 and an opposite second bolt portion 5 extending outwards of the plate. A first resonator element and a second resonator element are interposed between the first and second dielectric layers and are arranged in a spaced apart relationship from one another. The two detecting sections generate identical detection outputs when the foil strain gage is bonded on the strained section.