A test for screening defects of a transmission/reception circuit in an IC is enabled at low cost, without withstand voltage violation, and without carrying out electrical contacts with many terminals connected to oscillators. In a transmission/reception separation switch circuit using transistors as switch elements, a potential of a gate is lowered in a test more than the potential in a case of reception to avoid gate-source withstand-voltage violation when a large-amplitude signal is input, and an internal-signal loopback test is carried out without destroying a reception circuit.
