PURPOSE: To obtain a control circuit which is inexpensive and small in size, and has a sufficient automatic frequency control characteristic, by detecting a pilot signal by an output signal from a low-pass filter, being a control signal of a variable gain amplifier of an automatic gain control loop consisting of a narrow-band filter, a level detector, and the low-pass filter.

CONSTITUTION: In case the band width of a narrow-band filter 6 is the same or wider as or than a carrier wave-to-noise ratio, whether a pilot signal exists or not cannot be detected by a control signal of an output of the narrow-band filter 6, therefore, the band width of the narrow-band filter 6 is selected so as to become narrow enough against the carrier wave-to-noise ratio. As a result, in case of only a noise 3, and in case the pilot signal is contained, a control signal of a low-pass filter 18 is different, therefore, the pilot signal is caught even under the conditions of a level variation of the pilot signal and a low carrier wave-to-noise ratio, can be shifted to a synchronizing process of an automatic frequency control loop by controlling a sweep signal oscillator 14, and in the end, a synchronizing establishment is executed.