PURPOSE: To warrant stable operation by applying the frequency control of a temperature compensation type piezoelectric oscillation circuit at nontransmission or nonreception state of a communication equipment and not applying the frequency control at the transmission or reception.

CONSTITUTION: A timing for the frequency control of a temperature compensation type piezoelectric oscillation circuit 11 is controlled by an external control circuit 27 to apply the frequency control of the temperature compensation type piezoelectric oscillation circuit 11 when no adverse effect is given onto the communication of the communication equipment, that is, at nontransmission or nonreception and not to apply the frequency control at transmission or reception. Thus, even when frequency fluctuation or phase fluctuation takes place at the frequency control, or even when fluctuation is large, no adverse effect on the communication is caused.