This invention provides an adhesive hydrogel that has low contact resistance against the body surface and excellent conformability and adhesiveness to the body surface, so that noise generation can be reduced. In particular, such adhesive hydrogel enables measurements of weak fetal heart rate signals. The adhesive hydrogel according to the invention comprises a polymer matrix prepared by crosslinking-copolymerization of an acrylamide derivative, which is a nonionic polymerizable monomer comprising a polymerizable carbon-carbon double bond in a molecule, and polyfunctional (meth)acrylamide, which is a crosslinkable monomer comprising 2 or more polymerizable carbon-carbon double bonds in a molecule, water, a polyvalent alcohol, and an electrolyte salt, wherein a laminate of the adhesive hydrogel with an Ag/AgCl sheet exhibits the impedance of 1 Ω to 100 Ω at the frequency of 0.1 Hz measured in accordance with the method of ANSI/AAMI EC12:2000, and the dynamic elastic modulus G' at the frequency of 1 Hz measured at 25°C and dispersed frequencies is 1.0×103Pa to 1.0×104Pa.
