Directional coupler

A directional coupler (1) includes a substrate (10), a main line (20) formed directly or indirectly on the substrate (10), sub-lines (21, 22 and 23) at least part of each of which is formed directly or indirectly on the substrate (10) along the main line (20), a switch (30) switching connections among end portions of the plurality of sub-lines (21, 22 and 23), and detection output terminals (FWD and REV) connected to the sub-line (21), wherein, when looking at the substrate (10) in plan, the end portions of the sub-lines (21, 22 and 23) are disposed on the same side as the detection output terminals (FWD and REV) relative to the main line (20), and the sub-line (21) to which the detection output terminals (FWD and REV) are connected is overlapped with or surrounded by the sub-lines (22 and 23).