A directional coupler capable of improving a directionality of a directional coupler body including four terminals. The directional coupler includes a directional coupler body including the four terminals of an input port, an output port, a coupling port, and an isolation port; and a combiner for combining powers of an output signal of the coupling port and an output signal of the isolation port of the directional coupler body; and a directionality improving circuit for amplifying or attenuating at least one of the output signal of the coupling port and the output signal of the isolation port before outputting the same, and the combiner combines powers of the output signals amplified or attenuated by the directionality improving circuit.