increases suddenly to the value of the supply voltage which is v cc the collector of the transistor 56 is connected to the base of the transistor 64 so that the collector voltage increment is directly transferred to the base of the transistor 64 thus the emitter voltage of the transistor 64 follows the base voltage thereof and produces the leading edge of the pulse p d shown in fig5 c later when the voltage across the integrating capacitor 54 has decreased sufficiently following the end of the pulse p h in fig5 a the value of the integrated signal s i drops below the turn off voltage of the schmitt trigger which is approximately at the level e s or a little below that level and causes the state of conductivity of the transistors 55 and 56 to reverse back to their original condition this produces the trailing edge of the pulse p d as shown in fig5 c the pulse p d is supplied through the emitter follower circuit to the mixer circuit 6 there to be combined with the composite video signal the combined signal is applied to the peak detector circuit 7 and the output signal of that circuit controls the amplitude of the composite video signal s y by controlling the gain of the amplifier 2 in the same manner as in fig1 according to the present invention the effect of integrating the synchronizing pulse signal p h instead of differentiating it is.