A mixer for use in a double superheterodyne tuner which can receive either ground broadcasting channels or the satellite broadcasting channels is provided with frequency mixing diodes for the ground broadcasting signal and frequency mixing diodes for the satellite broadcasting signal. Switching diodes are provided between each of the frequency mixing diodes and output terminals of a balun transformer having an input terminal for receiving a local oscillation signal. When the ground broadcasting signal is received, the switching diodes connected to the frequency mixing diodes of the ground broadcasting are turned ON, with the switching diodes connected to the frequency mixing diodes of the satellite broadcasting are turned OFF, so that the leakage of the local oscillation signal to the satellite broadcasting signal when the ground broadcast signal is received is greatly reduced.