PURPOSE: To achieve a facilitating of measurement of an elongation-contraction of a ceramic wall plate in micron and moreover, an automation of the measurement for a long time.

CONSTITUTION: A metal plate 3 is arranged at both ends of a ceramic wall plate W fixed between supports 2... in such a manner that an eddy current is generated by an action of inducing an electromagnetic induction and an electromagnetic coil 4 is arranged facing the metal plate 3 being supported with a base other than the wall plate W. A high frequency excitation current is fed to the electromagnetic coil 4 to measure an interval between the metal plate 3 and the electromagnetic coil 4 depending on consumed oscillation energy of the electromagnetic coil 4 as medium by the eddy current generated in the metal plate 3 thereby achieving a measurement of an elongation-contraction of the wall plate.