PURPOSE: To dispense with not only the remote transmission of a clock signal but also a transmitting line, an exciter, an equalizer and an amplifier, by using the synchronous signal formed from the reference trigger signal in a composite video signal transmitted to generate the clock signal in a signal judge device.

CONSTITUTION: A clock signal generator 4 receives the synchronous signal from a synchronous signal generator to generate a clock signal which is, in turn, sent out to a signal judge device 5 while the number of clock signals are counted by a trigger generator 13 to generate a judging trigger signal for detecting an error when angle data coincides with a data length to sent out the same to the signal judge device 5. The signal judge device inputs the angle data from a signal selector 3, the clock signal from the clock signal generator 4 and the judging trigger signal to detect the error of the angle data and a quality judge signal is generated on the basis of the detection result to be sent to an output terminal.