A directional coupler is configured so as to include: a resistive element in which one end thereof is connected to a first terminal and the other end is connected to a second terminal; a first amplifier circuit for outputting either a current directly proportional to a first voltage applied to the one end of the resistive element or a current directly proportional to a second voltage applied to the other end of the resistive element; a second amplifier circuit for outputting a first current which is directly proportional to the voltage difference between the first voltage applied to the one end of the resistive element and the second voltage applied to the other end of the resistive element and whose polarity is different from that of the current outputted from the first amplifier circuit when a signal is flowing from the first terminal to the second terminal, and for outputting a second current which is directly proportional to the voltage difference between the first voltage and the second voltage and whose polarity is identical to that of the current outputted from the first amplifier circuit when a signal is flowing from the second terminal to the first terminal; and a first adder circuit for outputting either a signal having a voltage value directly proportional to a current which is the sum total of the current outputted from the first amplifier circuit and the first current or a signal having a voltage value directly proportional to a current which is the sum total of the current outputted from the first amplifier circuit and the second current to a third terminal.