A directional coupler with a high coupling per unit area and small variations in characteristic at manufacturing capable of achieving a high directivity easily and an RF circuit module provided with the directional coupler are achieved. A main-line is provided on a front surface of a multi-layer substrate, a ground plane is provided on a back surface of the multi-layer substrate. On an inner layer immediately under the main-line, two lines in parallel with the main-line are provided, and one line is provided on a layer closer to the ground plane than the two lines. By connecting the two lines and the one line with vias, a sub-line with a shape of a winding of a loop is formed. In the sub-line, a main component of a vector vertically penetrating the loop is horizontal with respect to the ground plane.