A directional coupler includes a main line and a subline. The main line connects an input port and an output port. The subline connects a coupling port and a terminal port. The subline includes a first coupling line section connected to the terminal port, a second coupling line section connected to the coupling port, and a low-pass filter. The low-pass filter includes an inductor provided between the first and second coupling line sections, a first capacitor having an end connected to the connection point between the inductor and the second coupling line section, a resistor connecting the other end of the first capacitor to the ground, and a second capacitor connecting the connection point between the inductor and the first coupling line section to the ground.