A balun comprises an unbalanced terminal, two balanced terminals, and two ground terminals. The balun further comprises: a low-pass filter provided between the unbalanced terminal and one of the balanced terminals; and a high-pass filter provided between the unbalanced terminal and the other of the balanced terminals. The low-pass filter incorporates two coils and a capacitor. The high-pass filter incorporates two capacitors and a coil. The coils and the capacitors are made up of conductor layers of a multi-layer substrate.