Abstract: The present invention provides a coupler having a high degree of coupling. The coupler comprises first and second dielectric substrates (141) and (142) each having first and second surfaces which are parallel to each other, a ground conductor (103) which is formed on the first surface of the first dielectric substrate (141), and two coupling line conductors (120) and (121) which are formed on the second surface of the second dielectric substrate (142) close to each other so as to be electromagnetically coupled to each other, wherein via conductors (150)˜(163) and (170)˜(183) which are filled in through holes passing through the second dielectric substrate are placed and connected to the two coupling line conductors (120) and (121) so as to enhance the degree of electromagnetic coupling, thereby increasing the opposing areas between the coupling line conductors (120) and (121) to increase the capacitance.