PURPOSE: To eliminate the need for balance adjustment of a mixer and enable a peripheral circuit to be simplified by calculating phase difference of input and output waves of a mixer based on the A/D converted data.

CONSTITUTION: Input/output waves of a high-frequency amplification circuit 1 are detected by couplers 8a and 8b. Then, an input Q (input of orthogonal component from output wave) and an input I (in-phase component input from in-phase component/orthogonal component coupler) are selected in time- multiplexed manner by a high-frequency switch at a specified timing of a timing generation circuit 4 and then it is mixed with a high-frequency signal RF from the input wave by a mixer 2. This signal IF is amplified 3 and then is A/D converted 5, which is latched 6 simultaneously for the output Q and the output I. Phase of this data is calculated 7, thus enabling a circuit to be simplified, circuit cost to be reduced, and eliminating the need for balance adjustment operation of the mixer 2.