PROBLEM TO BE SOLVED: To improve adhesiveness of an electrode unit to a living body while meeting a request for size reduction.SOLUTION: A gel member 5 attached to a base material 2 so as to cover an electrode element 3 disposed on the base material 2, has adhesiveness and conductivity. A portion 5a of the gel member 5 covering the electrode element 3 is at least partially reduced in thickness than a peripheral edge 5b.