PURPOSE: To correct the phase variation between a sum and a difference channels even during signal reception by generating a calibrating signal of frequency outside a reception band in addition to a signal of reception center frequency.

CONSTITUTION: A calibrating signal generator 15 selects and inputs a local signal f1 for reception center frequency generation when a preliminary check is performed and inputs a local signal f2 for reception out-band signal generation when data from an air frame is received, thereby generating calibrating signals respectively. Those calibrating signals are sent out to the difference and sum channels through a divider 14 and difference/sum channel directional couplers 1 and 7. Then the sum and difference channels, the tracking system composed of an automatic antenna tracking receiver 6, and a data demodulation system are checked with the signal f1. A sum/difference channel phase difference detector 12 detects a phase difference with the signal f2 and then difference/sum channel band-pass filters 5 and 1 perform sufficient attenuation. Therefore, the correction is performed in real time without exerting any influence upon the characteristics of the receiver 6.