PURPOSE: To make it possible to measure the tensile rigidity at an arbitrary part simply, by constituting a compressing piece, which is contacted with a material to be measured and compresses the material, by a load to voltage converter and an acceleration to voltage converter; integrating the speed signal from the acceleration converter twice; thereby converting the signal to a displacement signal.

CONSTITUTION: When a compressing piece 11 is compressed to a door panel 8, an electric signal is obtained from a load to voltage converter 3 in response to a load. An acceleration signal is obtained from an acceleration to voltage converter 12 in response to deforming acceleration of a panel 8. In order to integrate the signal twice and to convert the signal to a displacement signal, the load signal from a preamplifier 14 is compared with a preset value in a comparator 17. When the signal exceeds the preset value, an operating circuit 20 is operated, and a control circuit 19 is controlled so that the measured value is outputted from an amplifier circuit 16. The load signal from the preamplifier 14 and the displacement signal from the operating circuit 20 are inputted to an XY recorder 10 through the amplifier 16 and recorded as the load displacement curve diagram of the panel 8.