A directional coupler to be used in a predetermined frequency band, comprising: first to fifth terminals (14a to 14e); a main line that is connected between the first terminal and the second terminal; a first sub-line (S, S1) that is connected between the third terminal and the fourth terminal and that is electromagnetically coupled with the main line; and a first low pass filter, wherein the first terminal is an input terminal to which a signal is input, the second terminal is a first output terminal from which the signal is output, the third terminal is a second output terminal from which a signal having a power that is proportional to the power of the signal is output, the fourth terminal is a termination terminal that is terminated, and the fifth terminal is a ground terminal, a first low pass filter connected between the third terminal and the first sub-line (S, S1) and has a characteristic that attenuation increases with increasing frequency in the predetermined frequency band, wherein the first low pass filter includes a first coil that is connected in series between the third terminal and the first sub-line (S, S1), and a first capacitor, and wherein the first capacitor is connected between a point between the first coil and the first sub-line (S, S1), and the fifth terminal, characterized in that in the predetermined frequency band, the average value of the slope of the degree of coupling characteristic for a section of the directional coupler excluding the low pass filter and the average value of the slope of the insertion loss characteristic of the low pass filter have opposite signs and have substantially equal absolute values. first to fifth terminals (14a to 14e); a main line that is connected between the first terminal and the second terminal; a first sub-line (S, S1) that is connected between the third terminal and the fourth terminal and that is electromagnetically coupled with the main line; and a first low pass filter, wherein the first terminal is an input terminal to which a signal is input, the second terminal is a first output terminal from which the signal is output, the third terminal is a second output terminal from which a signal having a power that is proportional to the power of the signal is output, the fourth terminal is a termination terminal that is terminated, and the fifth terminal is a ground terminal, a first low pass filter connected between the third terminal and the first sub-line (S, S1) and has a characteristic that attenuation increases with increasing frequency in the predetermined frequency band, wherein the first low pass filter includes a first coil that is connected in series between the third terminal and the first sub-line (S, S1), and a first capacitor, and wherein the first capacitor is connected between a point between the first coil and the first sub-line (S, S1), and the fifth terminal, characterized in that in the predetermined frequency band, the average value of the slope of the degree of coupling characteristic for a section of the directional coupler excluding the low pass filter and the average value of the slope of the insertion loss characteristic of the low pass filter have opposite signs and have substantially equal absolute values.