A directional coupler (1) includes a surface mounted component (10) and a mounting substrate (20) on which the surface mounted component (10) is mounted. Among a main line and a sub line of the directional coupler (1), the main line is formed of a first line (31) and a second line (32), one end (311) of the first line (31) and one end (321) of the second line (32) being connected to each other, the sub line is formed of a third line (33). The first line (31) and the third line (33) are formed in the surface mounted component (10). The second line (32) is formed on or in the mounting substrate (20). Furthermore, another end (312) of the first line (31) and another end (322) of the second line (32) may be connected to each other.