The AC detection coil is a toroidal coil and includes plural radial-line conductors which are formed on a front face and a rear face of a substrate, conductive connection parts and conductive through-holes which connect electrically each end of radial-line conductors, wherein plural winding turns are consecutively formed by a connection of each radial-line conductor on the front and the rear faces, respectively, and include a forward coil and a backward coil, and each shape on the front and the rear faces of the radial-line conductors and the conductive connection parts are identical with each other. Consequently, when seen from a thickness direction of the substrate, areas of the forward coil and the backward coil are equal to each other, and an external, unneeded to be detected, magnetic field can be canceled each other by the forward coil and the backward coil, then a current detection accuracy can be improved.
