PURPOSE: To provide a microstrip line type coupler of a microwave circuit which can easily improve the control accuracy of the degree of coupling to a main signal tranmission circuit together with omission of the control trouble, and can keep the impedance of the main signal circuit at a prescribed level with its charqacteristic assured.

CONSTITUTION: A main signal transmission line 1 consists of a conductor pattern formed on a dielectric substrate 2 having an earth surface 5. A coupling line 3 is connected to a main signal via a conductor pattern formed on another dielectric substrate 4. The substrate 4 of the line 3 is movable to the substrate 2 of the line 1 so that the degree of couling varies between the conductor pattern of the line 3 and that of the line 1.