A nonreciprocal transmission line apparatus is provided with a cascade connection of unit cells between ports. Each unit cell includes a transmission line part for a microwave signal, and shunt branch circuits equivalently including inductive elements. Each unit cells has spontaneous magnetization or is magnetized by an external magnetic field so as to have gyrotropy by being magnetized in a magnetization direction different from a propagation direction of the transmission line part. In each of the unit cells, the shunt branch circuits includes a first stub conductor formed on one side with respect to a plane composed of the propagation direction and the magnetization direction, and a second stub conductor formed on the other side with respect to the plane, and the stub conductors have different electric length from each other.