A non-reciprocal circuit device comprising a magnetic plate F1; center conductors L1, L2, and L3 that are mutually insulated and disposed so as to intersect on magnetic plate F1; a plane conductor P1 that is disposed facing the center conductors with magnetic plate F1 placed therebetween, the plane conductor being connected to first ends of all the center conductors; matching capacitors C1 to C3 that have first ends grounded electrically and second ends connected to second ends of the center conductors; first matching circuits that have first ends connected to the second ends of the center conductors and second ends that are input/output ports; and a second matching circuit that has a first end connected to or integrated with the plane conductor and a second end grounded electrically.