PURPOSE: To prevent the fluctuation in the oscillated frequency of an oscillation circuit due to on/off of an amplifier circuit by terminating the output of the oscillation circuit when the amplifier circuit is turned off.

CONSTITUTION: The circuit consists of a two-distribution circuit 2 connecting to an output of an oscillation circuit 1, a 1st signal control circuit 3 whose input connects to a 1st output of the two-distribution circuit 2 and whose output connects to an input of an amplifier circuit 7, a 2nd signal control circuit 4 whose input connects to a 2nd output of the two-distribution circuit 2, a termination circuit 5 connecting to the output of the 2nd signal control circuit 4 and a changeover circuit 6 controlling the 1st and 2nd signal control circuits 3, 4. Then the output of the oscillation circuit 1 is terminated when the amplifier circuit 7 is turned off. Thus, the fluctuation of the oscillated frequency of the oscillation circuit 1 due to turn-on/off of the amplifier circuit 7 is prevented.