PURPOSE: To reduce the test time of a line identification circuit by eliminating a horizontal period pulse impressing to a flip-flop only for one horizontal period so as to change the inverted polarity of the flip-flop.

CONSTITUTION: In closing a switch 34, a voltage at an input terminal 41 is increased from 0V. A one-shot multivibrator 37 is activated, its output is brought from a low level into a high level so as to conduct a transistor (TR) 39. When the TR39 is conducted, an input terminal 33 of the line identification circuit 32 goes to 0V and no horizontal period pulse 30 is inputted. Since the pulse width of the vibrator 37 is set to one horizontal period, only one pulse among pulses 30 is eliminated. Thus, since the flip-flop in the circuit 32 is not inverted only once, the signal of a subcarrier is brought into the relation of error to a burst signal entering at the phase of ±135° at each horizontal period.