To create signature data which certifies the time when information existed and add it to the information more efficiently than before. A time certification system for certifying the time when information existed, comprising: an identity certification data acquisition section for acquiring identity certification data generated based on the information to certify the identity of the information; a time certification data generation section for observing a target object changing with time elapse from the outside and generating time certification data based on observation data obtained as a result of the observation, in response to an instruction received from a user; a signature data generation section for generating signature data indicating that the information existed at the time when the target object was observed, based on combination of the identity certification data and the time certification data; and an information recording section for recording the signature data in association with the information.