A transconductance amplifier is provided with: a cross-coupled differential pair (31) having one set of differential pair transistors in which signals whose polarities are opposite to each other are inputted to gates thereof, drains of one of the differential pair transistors being connected to drains of another one of the differential pair transistors, and a control circuit (32) comprised of logical circuits, for outputting a binary signal to the common source of each of the differential pair transistors on the basis of an output-level control signal and a polarity control signal which are inputted thereto.