To prevent the delay of phase pull-in time by performing feedback control for keeping the output voltage of a loop filter at a prescribed value and starting the operation of a voltage controlled oscillator based on the output voltage.

A control part 13 monitors the phase difference of the output of a reference frequency divider 2 and the output of a variable frequency divider 6, and at the time of detecting that the phase difference is zero for a fixed period, closes a second loop opening/closing switch 14 and stops the operation of a reset circuit 8. A first loop opening/closing switch 7 is short-circuited, a voltage holding circuit opening/closing switch 12 is opened, the operations of a D/A conversion part and a comparison part inside an arithmetic part 11 are stopped and the operation of a storage part is started. Similarly, the operation of an A/D converter 10 is started. The control part 13 detects the output voltage of the loop filter 4 in the operation period of respective circuit blocks. The delay of the phase pull-in time due to the decline of the output voltage of the loop filter 4 from standby period and operation period transition start until the rise of the voltage controlled oscillator 5 during an intermittent operation is prevented.