PURPOSE: To detect the abnormality of a current lead itself occurring at current application at an early stage by attaching a light waveguide part to the conductor wire of a conductor, which constitutes a current lead, and allowing light to enter this light waveguide part, and detecting the change of intensity, wavelength, etc., of the light having come out.

CONSTITUTION: An insulator 5 surrounds a conductor wire 3 and a light waveguide 4, and further these are attached to the supporter 2 lying at the roughly center of a hollow tube 1. And, at least one conductor consisting of such conductor wire 3 and the light waveguide 4 into the hollow tube 1 so as to constitute a current lead. Since the conductor wire 3 and the light waveguide 4 are positioned closely, if unequal partial heating occurs in the conductor wire 3, the light waveguide 4 is partially deformed, too, by the thermal expansion of the conductor wire 3. It becomes possible to detect the abnormality of the current lead itself at an early stage by optically detecting the deformation occurring in this light waveguide 4.