In a device which is supplied with a compression coded signal given by subjecting an original video signal to differential coding and which includes a converting section (10, 8, 7, 6) for carrying out a converting operation of converting the compression coded signal into a DCT coded signal identical with a coded signal given by subjecting the original video signal to DCT coding, a timer (3) measures a total time interval as a measured time interval until a reproducing unit (20) finishes reproducing from the DCT coded signal a leading frame of the original video signal from a time instant at which the converting section starts the converting operation. A subsampling information producing circuit (13) produces optimum subsampling information with reference to the measured time interval to make the converting section carry out an optimum subsampled converting operation of converting remaining frames of the compression coded signal into the DCT coded signal in accordance with the optimum subsampling information. Preferably, the subsampling information producing circuit compares the measured time interval with a predetermined time interval and produces, when the measured time interval is greater than the predetermined time interval, first subsampling information as the optimum subsampling information to make the converting section carry out a simplified subsampled converting operation as the optimum subsampled converting operation in accordance with the first subsampling information.