PURPOSE: To detect simply and highly precisely a displacement due to variations of volume and temp. caused by hardening reaction by adhering a magnetic material whose magnetic characteristic is varied by stress to a thermoplastic polymer material or a thermosetting polymer material capable of polymerizing by the reaction, and detecting an extent of displacement of the high polymer material with the variation of the magnetic characteristic of the magnetic material.

CONSTITUTION: The material of a sample case 4 filling the high polymer material or monomer consists of a nonmagnetic material which is not deformed and deteriorated within a temp. range of measurement. In case the material of sample case has a large adhesive strength against the sample 5 or the influence of the adhesion is desired to be small, a mold release layer efficient to the sample is formed to the inner surface. An amorphous alloy capable of adjusting easily the magnetostriction constant by varying the composition corresponding to the extent of displacement of the polymer material to be measured and capable of varying magnetic characteristic such as magnetic permeability remarkably due to the strain is suitable to a sensor material 6, but the material is not restricted by said alloy. Since Young's modulus of polymer, e.g. epoxy resin is about 250kg/mm2 and that of the material 6, e.g. amorphous alloy is about 12,000kg/mm2, the extent of variation of the material 6 corresponding to the displacement of the polymer material is extremely small.