PURPOSE: To stabilize a local oscillating frequency to any temperature change by detecting an internal temperature at the operation of a local oscillator as an electric signal and feeding back this signal to a comparator.

CONSTITUTION: If the internal temperature of the local oscillator 7 is changed, a temperature detector 8 converts this temperature change into a voltage change and outputs the result to a temperature correcting device 9. The device 9 outputs an error voltage and a voltage proportional to the characteristic of the local oscillating frequency to a comparator 6b. The comparator 6b compares this signal with a reference signal from a reference signal generator 5 and outputs the error voltage to the device 7. As a result, the local oscillating frequency of the device 7 becomes F+FIF[Hz] (where; F is a frequency of a receiving signal and FIF is an intermediate frequency of the device 4), and even if the internal temperature of the device 7 is changed, an automatic frequency controller 1 continues the operation.