A power amplifying circuit includes a first amplifier, a second amplifier, a transformer having a primary winding and a secondary winding, and a capacitor. The first amplifier amplifies a signal which is one of differential signals. The second amplifier amplifies a signal which is the other of the differential signals. The primary winding is connected, at its first end, to the first amplifier, and is connected, at its second end, to the second amplifier. The secondary winding is connected, at its first end, to an unbalanced line through which an unbalanced signal is transmitted, and is connected, at its second end, to the ground. The secondary winding is electromagnetically coupled to the primary winding. The capacitor is connected, at its first end, to the midpoint of the primary winding, and is connected, at its second end, to the ground.