In a time stamping system formed by a client device and a server device, the client device includes a digest generation unit for generating a plurality of digests for a plurality of digital documents, a digest combining unit for combining the plurality of digests generated by the digest generation unit, a unified digest generation unit for generating a unified digest from the plurality of digests as combined by the digest combining unit, a transmission unit for transmitting a time stamping request containing the unified digest generated by the unified digest generation unit, to the server device, and a reception unit for receiving a time stamp token for the plurality of digital documents from the server device. The server device generates the time stamp token containing a time stamped digital document obtained by combining the unified digest and a time information acquired in response to the time stamping request, and a digital signature for the time stamped digital document.