PURPOSE: To prevent the evil effect of the dropout to the generation of the reading clock by producing the reading clock through the fixed free-running circuit.

CONSTITUTION: Vertical synchronous signal Sb isolated from the reproduced PCM video signal receives the delay of a fixed time via V delay circuit F, and then signal Sc equivalent to start signal Sd isolated through delay circuit A is generated. Thus even if signal Sd lacks due to the dropout or the like, signal Sc resets H counter G via OR circuit E. As a result, counter G has the free running via oscillator C to generate the reading clock with no evil effect given by the dropout, thus securing the assured reading for the fixed number of the data groups. The free-running counter G is stopped via V counter H and others after counting the fixed number of the data groups.