An input-output balanced filter has a greatly reduced size and excellent stable electric characteristics. The input-output balanced filter includes two LC bandpass filter circuit units. A first LC bandpass filter circuit unit has a circuit structure in which a first LC parallel resonant circuit including an inductor and a capacitor is connected to a second LC parallel resonant circuit including an inductor and a capacitor via a connecting capacitor, while the second LC bandpass filter circuit unit has a circuit structure in which a third LC parallel resonant circuit including an inductor and a capacitor is connected to a fourth LC parallel resonant circuit including an inductor and a capacitor via the other connecting capacitor; and, the common side lines of the two LC bandpass filter circuit units are connected to each other via a connecting inductor which functions as a common line.