improve peelability of the hydrogel pad from the body after use at least one layer composed of woven fabric or net like nonwoven fabric is placed in the hydrogel pad the arrangement of the woven fabric or net like nonwoven fabric supports the hydrogel pad which results in easy handling prevents self adhesion of hydrogels which forms a spherical shape during handling and prevents elongation of the hydrogel pad when peeling it off from the skin therefore it is desired for the fabric to have a repulsion force in a certain degree the mesh size of the woven fabric or net like nonwoven fabric is from about 0 1 to 5 0 mm if the mesh size is less than about 0 1 mm the hydrogel does not sufficiently permeate into the fabric and as a result the electric current flow passage is disturbed and consequently electrical noise causes during measurement on the other hand if the mesh size is larger than about 5 0 mm the self supporting property of the fabric is poor the thickness of the woven fabric or net like nonwoven fabric is not particularly limited but from a practical viewpoint it generally from about 50 to 400 u03bc the material of the woven fabric and net like nonwoven fabric is not particularly limited and any conventional natural and synthetic fibers can be used representative examples thereof are polyesters rayon and the like preferably two layers of the woven fabric or net like nonwoven fabric are arranged near the surfaces of the hydrogel pad a representative.