A signature generating device includes a receiving unit that receives a sequence of data; a summary data generating unit that generates summary data of the data upon reception of each of the data by the receiving unit; an obtaining unit that obtains, when the number of data included in a sequence of the generated summary data reaches a given number, the sequence of the summary data as a block; a setting unit that sets, as a signature subject, a current block constituted by the sequence of the summary data, and the summary data selected from at least one block contiguous to the current block; a digital signature generating unit that generates a digital signature concerning data summarized for the current block; and a sending unit that sends the generated digital signature, the signature subject associated with the digital signature, and the data summarized for the current block.