A non-reciprocal circuit device comprising a first inductance element disposed between a first input/output port and a second input/output port, a second inductance element disposed between the second input/output port and a ground, a first capacitance element constituting a first parallel resonance circuit with the first inductance element, a second capacitance element constituting a second parallel resonance circuit with the second inductance element, a resistance element parallel-connected to the first parallel resonance circuit, and an impedance-adjusting means disposed between the first input/output port and the first inductance element.