Abstract: There is disclosed a horizontal synchronizing signal generating circuit for generating a horizontal synchronizing signal which has no frequency variations and which is in phase with an entered composite synchronizing signal if the entered composite synchronizing signal is a nonstandard signal having a varying horizontal frequency. A horizontal counter circuit (5) counts a reference clock (V.sub.CL), and a window pulse generating circuit (4) outputs a window pulse signal (V.sub.W) which is low for a fixed time period when a counter output (V.sub.CT) equals a counter value (878) indicative of a standard output timing. A horizontal synchronizing signal separating circuit (1) outputs a horizontal synchronizing signal (V.sub.2) only when the composite synchronizing signal (V.sub.1) falls within the fixed time period. Then a horizontal phase judging circuit (2) outputs a standard signal flag (V.sub.3) and a synchronizing signal generating circuit (3) outputs the horizontal synchronizing signal (V.sub.

Abstract: A sampling circuit is not susceptible to an influence of structural components and environmental changes. A phase difference detecting circuit (5) detects a deviation of a sampling clock (.phi.2) from optimal sampling timing and outputs a phase difference signal. On the other hand, a phase reference signal (ORG) which is used as a reference to determine a phase advance and a phase lag is generated by a phase reference detecting circuit (4). In accordance with these signals, a sampling clock shifting circuit (2) shifts the sampling clock (.phi.2) so that the sampling clock (.phi.2) is activated at optimal sampling timing. Sampling is performed in accordance with such a sampling clock (.phi.2), whereby a basic signal is generated from which the phase reference signal (ORG) and the phase difference signal (i.e., an equivalent signal (EQU) and a non-equivalent signal (UPDN)) are generated. By means of feedback control, the sampling clock is automatically activated at optimal sampling timing.