Abstract: A similar-information search method includes obtaining an instruction indicating which of an encrypted search and an unencrypted search a data computation device is to perform; generating an encrypted feature quantity and transmitting the encrypted feature quantity to the data computation device; generating an encrypted similarity value and transmitting the encrypted similarity value; and receiving encrypted reference data from the data computation device and decrypting the encrypted reference data. A homomorphic encryption scheme that makes decryption by the data computation device unsuccessful is used when the encrypted search is performed, whereas an encryption scheme that makes decryption by the data computation device successful is used when the unencrypted search is performed.