A key cloud system comprising: a client device; a directory service device having a storage; and a plurality of key cloud devices (15-j); wherein encryption keys EK(j) correspond to decryption keys DK(j), each of the encryption keys EK(j) is public information, each of the decryption keys DK(j) is secret information, j∈{1,..., J}, and J≥2; each of the key cloud devices (15-j) stores each of the decryption keys DK(j), and provides a cloud-key management type decryption service in which each of the decryption keys DK(j) is used; and the directory service device generates name information N(j) corresponding to each of the key cloud devices (15-j) by using each of the encryption keys EK(j), and stores the name information N(j) and address information A(j) of each of the key cloud devices (15-j) in the storage in a manner to associate the name information N(j) with the address information A(j); characterized in that: an encrypted content C(i) encrypted with an encryption key EK(i) is input into the client device where i∈{1,..., J} and the encryption key EK(i) is embedded in the encrypted content C(i); the client device generates name information N(i) by using the encryption key EK(i) which is embedded in the encrypted content C(i), and outputs the name information N(i) to the directory service device; the directory service device searches the storage by using the name information N(i) to obtain address information A(i) of a key cloud device (15-i), the address information A(i) corresponding to the name information N(i), and outputs the address information A(i); the client device connects to the key cloud device (15-i) by using the address information A(i) which is input, and outputs perturbed information which is obtained by perturbing the encrypted content C(i) to the key cloud device (15-i) in order to receive the decryption service by the key cloud device (15-i); and the key cloud device (15-i) obtains the perturbed information and uses the decryption key DK(i) which is stored in the key cloud device (15-i) to provide the client device with information for obtaining a decryption value of the encrypted content C(i) in the client device by a self-correction technique. a client device; a directory service device having a storage; and a plurality of key cloud devices (15-j); wherein encryption keys EK(j) correspond to decryption keys DK(j), each of the encryption keys EK(j) is public information, each of the decryption keys DK(j) is secret information, j∈{1,..., J}, and J≥2; each of the key cloud devices (15-j) stores each of the decryption keys DK(j), and provides a cloud-key management type decryption service in which each of the decryption keys DK(j) is used; and the directory service device generates name information N(j) corresponding to each of the key cloud devices (15-j) by using each of the encryption keys EK(j), and stores the name information N(j) and address information A(j) of each of the key cloud devices (15-j) in the storage in a manner to associate the name information N(j) with the address information A(j); characterized in that: an encrypted content C(i) encrypted with an encryption key EK(i) is input into the client device where i∈{1,..., J} and the encryption key EK(i) is embedded in the encrypted content C(i); the client device generates name information N(i) by using the encryption key EK(i) which is embedded in the encrypted content C(i), and outputs the name information N(i) to the directory service device; the directory service device searches the storage by using the name information N(i) to obtain address information A(i) of a key cloud device (15-i), the address information A(i) corresponding to the name information N(i), and outputs the address information A(i); the client device connects to the key cloud device (15-i) by using the address information A(i) which is input, and outputs perturbed information which is obtained by perturbing the encrypted content C(i) to the key cloud device (15-i) in order to receive the decryption service by the key cloud device (15-i); and the key cloud device (15-i) obtains the perturbed information and uses the decryption key DK(i) which is stored in the key cloud device (15-i) to provide the client device with information for obtaining a decryption value of the encrypted content C(i) in the client device by a self-correction technique. an encrypted content C(i) encrypted with an encryption key EK(i) is input into the client device where i∈{1,..., J} and the encryption key EK(i) is embedded in the encrypted content C(i); the client device generates name information N(i) by using the encryption key EK(i) which is embedded in the encrypted content C(i), and outputs the name information N(i) to the directory service device; the directory service device searches the storage by using the name information N(i) to obtain address information A(i) of a key cloud device (15-i), the address information A(i) corresponding to the name information N(i), and outputs the address information A(i); the client device connects to the key cloud device (15-i) by using the address information A(i) which is input, and outputs perturbed information which is obtained by perturbing the encrypted content C(i) to the key cloud device (15-i) in order to receive the decryption service by the key cloud device (15-i); and the key cloud device (15-i) obtains the perturbed information and uses the decryption key DK(i) which is stored in the key cloud device (15-i) to provide the client device with information for obtaining a decryption value of the encrypted content C(i) in the client device by a self-correction technique.