A signature generating device (2) includes a collecting unit (11) configured to collect threat information, an extracting unit (21) configured to extract attack data from the threat information collected by the collecting unit (11), and a generating unit (31) configured to generate a signature on the basis of the attack data extracted by the extracting unit (21). When plural pieces of attack data having a common character string are extracted by the extracting unit (21), the generating unit (31) tentatively generates a signature including the common character string, evaluates whether a tentatively generated signature includes a character string used in non-attack data, and when the tentatively generated signature includes the character string used in the non-attack data, removes the character string from the tentatively generated signature to generate a signature.