A multimode frontend circuit comprising a first port, a second port and a third port, a first transmission path between the first and second ports, and a second transmission path between the first and third ports, characterized in that: each of the respective transmission paths comprises: two input/output lines (1103, 1104, 1203, 1204); a first transmission line (1101, 1201) having one end connected to one of the input/output lines and the other end connected to the other input/output line; a second transmission line (1102, 1202) having one end connected to the one of the input/output lines and the other end connected to the other input/output line; and one or a plurality of termination switch circuits (1110, 1210); and the electrical length of the first transmission line is equal to the electrical length of the second transmission line; a characteristic impedance for an even mode and a characteristic impedance for an odd mode of the first transmission line are constant along the length of the first transmission line; a characteristic impedance for an even mode and a characteristic impedance for an odd mode of the second transmission line are constant along the length of the second transmission line; the characteristic impedance for the even mode of the first transmission line is equal to the characteristic impedance for the even mode of the second transmission line; the characteristic impedance for the odd mode of the first transmission line is equal to the characteristic impedance for the odd mode of the second transmission line; each of the one or plurality of termination switch circuits comprises a switch (1111, 1211) and a termination circuit (1112, 1212), one end of the switch being connected to one of the first and second transmission lines, the termination circuit being connected to the other end of the switch; and the termination circuit changes the frequency characteristics of the respective transmission path according to the state of the switch. each of the respective transmission paths comprises: two input/output lines (1103, 1104, 1203, 1204); a first transmission line (1101, 1201) having one end connected to one of the input/output lines and the other end connected to the other input/output line; a second transmission line (1102, 1202) having one end connected to the one of the input/output lines and the other end connected to the other input/output line; and one or a plurality of termination switch circuits (1110, 1210); and the electrical length of the first transmission line is equal to the electrical length of the second transmission line; two input/output lines (1103, 1104, 1203, 1204); a first transmission line (1101, 1201) having one end connected to one of the input/output lines and the other end connected to the other input/output line; a second transmission line (1102, 1202) having one end connected to the one of the input/output lines and the other end connected to the other input/output line; and one or a plurality of termination switch circuits (1110, 1210); and the electrical length of the first transmission line is equal to the electrical length of the second transmission line; a characteristic impedance for an even mode and a characteristic impedance for an odd mode of the first transmission line are constant along the length of the first transmission line; a characteristic impedance for an even mode and a characteristic impedance for an odd mode of the second transmission line are constant along the length of the second transmission line; the characteristic impedance for the even mode of the first transmission line is equal to the characteristic impedance for the even mode of the second transmission line; the characteristic impedance for the odd mode of the first transmission line is equal to the characteristic impedance for the odd mode of the second transmission line; each of the one or plurality of termination switch circuits comprises a switch (1111, 1211) and a termination circuit (1112, 1212), one end of the switch being connected to one of the first and second transmission lines, the termination circuit being connected to the other end of the switch; and the termination circuit changes the frequency characteristics of the respective transmission path according to the state of the switch.