A central conductor assembly for a non-reciprocal circuit device, at least a first central conductor constituting a first inductance element and a second central conductor constituting a second inductance element being integrally formed in a laminate comprising pluralities of magnetic layers, the first central conductor being formed by series-connecting first and second lines formed on a first main surface of the laminate to third lines formed in the laminate through via-holes, and the second central conductor being formed on the first main surface of the laminate such that it extends between the first and second lines and crosses the third lines via a magnetic layer.