PURPOSE: To reduce malfunction due to noise, etc., by providing a discrimination circuit detecting the output of a lock detection section in a PLL detection circuit detecting a video intermediate frequency signal, and using the output of the discrimination circuit to search the tuning point.

CONSTITUTION: A discrimination circuit 11 consists of a comparator 21 whose one input terminal receives a reference voltage obtained by dividing a power supply +Vcc by resistors R1, R2 and whose other input terminal receives an output of a PLL lock detection section 10. Since the output of a comparator 21 is low when the output of the PLL lock detection section 10 is low, a microcomputer 1 in such a case quickens the increasing or decreasing speed of the tuning voltage to the tuner 5. Then the output of the PLL lock detection section 10 goes to a high level, the output of the comparator 21 goes to a high level, the microcomputer 1 slows down the increasing or decreasing speed of the tuning voltage to the tuner 5, the optimum tuning point is found out while the output of an AFT curve is being observed and the tuning voltage at this point of time is stored in a memory 2.