afc introducible range and the free running frequency controlling loop frl is operated step d fig3 a is a flowchart showing an example of operation of the free running frequency controlling loop frl first of all the free running frequency adjusting switch frsw is opened step e at this time the video image mute is effected if necessary then a frequency of a horizontal synchronous signal h sync and a frequency of free running horizontal driving signal hdo are measured step f these frequencies are compared with each other to obtain adjustment data and to apply a control voltage to the vco 2 1 through the dac 3 shown in fig1 thereby causing the frequency of free running horizontal driving signal hdo to approach the frequency of h sync routine g when the free running frequency sufficiently approaches the frequency of h sync the free running frequency adjusting switch frsw is closed step h at the same time if the video image mute is effected it is released the operation is returned back to the main routine shown in fig2 so that the normal horizontal scanning frequency controlling loop hfl is continued thus the horizontal scanning frequencies are suitably switched over relative to a video signal input having different horizontal scanning frequencies the routine g may be realized the following methods shown in for example fig5 and 6 to be described later first of all the free running frequency of hdo is roughly determined in accordance with a so called two division searching method which sets a destination datum to the average value of the two source data since hdo is controlled by the 8 bit dac 3 as shown in fig1 hdo can take only separate values subsequently.