This invention relates to a device of electrodes for measuring water content in foundry sand, an apparatus for measuring water content in foundry sand, and a method and an apparatus for supplying water to a sand mixer. When the prior art device for measuring water content in the foundry sand is disposed in it, the size or shape of the device of the electrodes is limited. To solve this problem, the device of the electrodes for measuring water content in the foundry sand by supplying an electric current to it is comprised of a plurality of conductive elements 2, 3 concentrically disposed with certain intervals between them in a longitudinal direction, wherein the elements form an annular shape, a retaining element 4 to retain the plurality of the conductive elements 2, 3, wherein the retaining element 4 has an electrical insulating property and a cylindrical shape having the same diameter as the conductive elements 2, 3, and the two conductive wires 5, 6 to connect alternate respective elements of the plurality of conductive elements 2, 3 so that the conductive elements 2, 3 form two poles, wherein the two conductive wires 5, 6 pass through the cavity in the retaining element 4.