the ptp save 30 is protected from developing malfunction due to the accumulated error in the restored clock value of u03b1 mhz the above embodiment was explained on the assumption that u03b1 mhz of the reference clock is 27 mhz alternatively this disclosure can also be applied to cases where u03b1 mhz is 33 mhz or some other suitable frequency in such cases however the table 54 above needs to retain the indicated correspondence with the 33 values for the embodiment above the order of the timestamp was shown to be in nanoseconds alternatively the order of the timestamp may be determined otherwise the series of the above described processes performed by the ns conversion processing part 13 a or by the ns reverse conversion processing part 33 a may be executed either by hardware or by software where the processes are to be carried out by software the programs constituting the software are installed into a suitable computer for execution such computers may include those with the software incorporated in their dedicated hardware beforehand and those such as general purpose personal computers or the like capable of executing diverse functions based on various programs installed therein fig1 is a block diagram showing a typical structure of a computer that executes the series of the above described processes using programs in this computer a cpu central processing.