PURPOSE: To improve detection accuracy by deforming a distortion plate where a strain gauge is provided constantly stably according to the displacement of an object to be measured.

CONSTITUTION: The title sensor is constituted so that it converts the displacement of a pick-up lever 8 which moves according to the displacement of an object 6 to be measured to a load by a coil spring 10 and the load is applied to a distortion plate 4 where a strain gauge 2 is provided via a spring holder 12. Then, by forming the center part receiving a load from the coil spring 10 and the outer-periphery part which is fixed to a base 14 of the distortion plate 4 thickly, the distortion plate 4 is formed in a beam structure where the center part and the outer-periphery part are connected by a thin plane beam and the strain gauge 2 is provided at the plane beam part, thus applying a load to the entire center part of the distortion plate 4, causing the plane beam part to be deformed stably constantly according to the displacement of the object 6 to be measured, and hence accurately detecting the displacement of the object 6 to be measured by the strain gauge 2.