A wireless circuit comprising: a transmission-reception antenna; a variable frequency duplexer having a common terminal connected to the transmission-reception antenna; a double-pole 2N-throw switch having two common contacts respectively connected to a transmission terminal and a reception terminal of the variable frequency duplexer, N being an integer not smaller than 1; a radio frequency integrated circuit, RFIC, which includes N transmission ports and N reception ports respectively connected to 2N transfer contacts of the switch; and a controller which is connected to the variable frequency duplexer and the switch through control lines and executes switching control operations of the switch and a frequency switching operation of the variable frequency duplexer in accordance with control signals; the RFIC comprises: a channel quality parameter measurement unit which measures channel quality parameters of all searched cells; a candidate cell determination unit which compares the measured channel quality parameter values with a predetermined threshold and extracts cells having channel quality parameter values exceeding the threshold as candidate cells; a pair determination unit which determines a combination of frequency bands that satisfy a given condition, of a candidate cell among the extracted candidate cells, as the pair of frequency bands for a transmission and a reception signal; and a control signal generation unit which generates and sends the control signals for performing the switching control operations to connect the transmission port corresponding to the determined transmission-signal frequency band with the transmission terminal of the variable frequency duplexer and to connect the reception port corresponding to the determined reception-signal frequency band with the reception terminal of the variable frequency duplexer and for performing the frequency switching operation of the variable frequency duplexer, characterized in that the given condition is determined in accordance with a frequency band separation coefficient θ 1 given by: θ 1 = 2 α 1 − β 1 α 1 + β 1 × 100 where α 1 is a boundary frequency of the transmission frequency band that is closer to the reception frequency band, and β 1 is a boundary frequency of the reception frequency band that is closer to the transmission frequency band. a transmission-reception antenna; a variable frequency duplexer having a common terminal connected to the transmission-reception antenna; a double-pole 2N-throw switch having two common contacts respectively connected to a transmission terminal and a reception terminal of the variable frequency duplexer, N being an integer not smaller than 1; a radio frequency integrated circuit, RFIC, which includes N transmission ports and N reception ports respectively connected to 2N transfer contacts of the switch; and a controller which is connected to the variable frequency duplexer and the switch through control lines and executes switching control operations of the switch and a frequency switching operation of the variable frequency duplexer in accordance with control signals; a channel quality parameter measurement unit which measures channel quality parameters of all searched cells; a candidate cell determination unit which compares the measured channel quality parameter values with a predetermined threshold and extracts cells having channel quality parameter values exceeding the threshold as candidate cells; a pair determination unit which determines a combination of frequency bands that satisfy a given condition, of a candidate cell among the extracted candidate cells, as the pair of frequency bands for a transmission and a reception signal; and a control signal generation unit which generates and sends the control signals for performing the switching control operations to connect the transmission port corresponding to the determined transmission-signal frequency band with the transmission terminal of the variable frequency duplexer and to connect the reception port corresponding to the determined reception-signal frequency band with the reception terminal of the variable frequency duplexer and for performing the frequency switching operation of the variable frequency duplexer,