In measuring the stress of a ferromagnetic linear metal member, an alternating current is supplied to flow between a pair of terminals mounted to the ferromagnetic linear metal member to measure an impedance .vertline.Z.vertline. of the ferromagnetic linear metal member between the terminals by an analyzer. Then, a stress .sigma. is determined based on the measured value of the impedance .vertline.Z.vertline. from an impedance .vertline.Z.vertline.-stress .sigma. relationship possessed by the ferromagnetic linear metal member. The stress distribution in a sheet-like sensor can be likewise measured by inserting into the sensor a plurality of intersecting ferromagnetic linear metal members. The stress .sigma. is determined for each individual member as described above, and then the stress distribution in the sheet-like sensor is determined by summing up the stresses of mutually intersecting members.