PURPOSE: To realize a wide range of bands for a rat race type directional coupler, by constituting so that the value of the characteristic addmittance of at least a part in an arc-shaped material having a length equivalent to 3/4 wavelength is different.

CONSTITUTION: The 4th arc-shaped material 4 having a 3λ0/4 length is divided with each λ0/4 length. A divided arc-shaped material 10 has the normalized characteristic addmittance value R4 which is different from other divided arc- shaped materials 9 and 11. The normalized addmittance value of each arm is set at Y1 to the 1st arc-shaped material 1, Y2 to the 2nd and 3rd arc-shaped materials 2 and 3, Y3 to the divided arc-shaped materials 9 and 11, and Y4 to the material 10 respectively. At the same time, each of arms 5∼8 has the normalized characteristic admittance value Y0. As a result, a wide range of bands is secured for a directional coupler.