PURPOSE: To eliminate the need for a through-hole forming in a substrate and the need for a complicated microwave circuit, by constituting a double balance type mixer with a microstrip circuit using only one side of a dielectric substance substrate.

CONSTITUTION: A signal input applied to a terminal 21 is applied to connecting points C and D with opposite phase. Since a circuit constituting mixer diodes 24, 25 and a 1/2 wavelength line 28 is symmetric to a CE axis, points A and B are at zero potential to a signal applied to a point C. This is the same as a circuit consisting of mixer diodes 26, 27 and a 1/2 wavelength line 29. Thus, a signal voltage shown in the dotted arrow is applied to diodes 24∼27. A local oscillation signal applied to a terminal 22 is applied to points A and A' with in- phase, the points B and B' are of the opposite phase with the points A and A' and points C∼F are at zero potential. Thus, a local oscillation voltage as shown in the solid-line arrow is applied to the diodes 24∼27. That is, this circuit acts as a double balance type mixer.