Patent ID: 7257393

Claim:
A time-stamping device that affixes a digital signature including a local time clocked by an internal clock to electronic data, the time-stamping device comprising: a radio-transmitted-time receiving unit that receives a standard time included in a radio wave as a radio-transmitted time; an authentic-time receiving unit that receives an authentic time synchronized with the standard time from a time server; a calculating unit that calculates an absolute value of a difference between the radio-transmitted time and the local time; a time modifying unit that modifies, when the absolute value calculated is less than a first threshold value, the local time by setting the radio-transmitted time as the local time, and leaves, when the absolute value calculated is equal to or greater than the first threshold value, the local time as it is; and a time correcting unit that corrects the local time based on the authentic time received; wherein the authentic-time receiving unit receives the authentic time from the time server when the absolute value calculated is less than the first threshold value a predetermined number of successive times.