A non-reciprocal circuit device comprising: a magnetic plate; a plurality of center conductors (L1, L2, L3), each of which has a first end and a second end, the plurality of center conductors being mutually insulated and disposed so as to intersect on the magnetic plate; a plane conductor disposed facing the plurality of center conductors (L1, L2, L3) with the magnetic plate placed between the plane conductor and the plurality of center conductors, the plane conductor being connected to the first ends of all of the plurality of center conductors; a plurality of matching capacitors (C1, C2, C3), each of which has a first end and a second end, the first end being grounded electrically, the second end being connected to the second end of a corresponding one of the plurality of center conductors (L1, L2, L3); a plurality of first matching circuits (M11, M12, M13), each of which has a first end and a second end, the first end being connected directly to the second end of a corresponding one of the plurality of center conductors (L1, L2, L3), the second end being an Input/output port (SS1, SS2, SS3); and a second matching circuit having a first end and a second end, the first end being connected to or integrated with the plane conductor, the second end being grounded electrically; characterised in that each of the plurality of the first matching circuits (M11, M12, M13) has at least a pair of a first inductor (L11, L12, L13) connected between the corresponding center conductor (L1, L2, L3) and the corresponding input/output port (SS1, SS2, SS3) and a first capacitor (C11, C12, C13) having a first end and a second end, the first end being connected to one end of the first inductor (L11, L12, L13) on the input/output port side, the second end being grounded, and the second matching circuit is a second capacitor; or has a second capacitor and a second inductor connected in series and said non-reciprocal circuit has a first operating frequency band determined mainly by said plurality of center conductors (L1, L2, L3), said plurality of matching capacitors (C1, C2, C3) and said plurality of first matching circuits (M11, M12, M13) and a second operating frequency band determined mainly by said plurality of first matching circuits (M11, M12, M13) and said second matching circuit apart from said first operating frequency band. a magnetic plate; a plurality of center conductors (L1, L2, L3), each of which has a first end and a second end, the plurality of center conductors being mutually insulated and disposed so as to intersect on the magnetic plate; a plane conductor disposed facing the plurality of center conductors (L1, L2, L3) with the magnetic plate placed between the plane conductor and the plurality of center conductors, the plane conductor being connected to the first ends of all of the plurality of center conductors; a plurality of matching capacitors (C1, C2, C3), each of which has a first end and a second end, the first end being grounded electrically, the second end being connected to the second end of a corresponding one of the plurality of center conductors (L1, L2, L3); a plurality of first matching circuits (M11, M12, M13), each of which has a first end and a second end, the first end being connected directly to the second end of a corresponding one of the plurality of center conductors (L1, L2, L3), the second end being an Input/output port (SS1, SS2, SS3); and a second matching circuit having a first end and a second end, the first end being connected to or integrated with the plane conductor, the second end being grounded electrically; characterised in that each of the plurality of the first matching circuits (M11, M12, M13) has at least a pair of a first inductor (L11, L12, L13) connected between the corresponding center conductor (L1, L2, L3) and the corresponding input/output port (SS1, SS2, SS3) and a first capacitor (C11, C12, C13) having a first end and a second end, the first end being connected to one end of the first inductor (L11, L12, L13) on the input/output port side, the second end being grounded, and the second matching circuit is a second capacitor; or has a second capacitor and a second inductor connected in series and said non-reciprocal circuit has a first operating frequency band determined mainly by said plurality of center conductors (L1, L2, L3), said plurality of matching capacitors (C1, C2, C3) and said plurality of first matching circuits (M11, M12, M13) and a second operating frequency band determined mainly by said plurality of first matching circuits (M11, M12, M13) and said second matching circuit apart from said first operating frequency band.