A re-encryption system comprising a file sharing apparatus and a re-encryption apparatus which are communicable with a client apparatus operated by a member belonging to a group, the file sharing apparatus comprising file storage means for storing an encrypted file including a first encrypted symmetric key portion obtained by encrypting a symmetric key based on a public key of the group and an encrypted data portion obtained by encrypting data based on the symmetric key, first means for acquiring, upon receiving a file request including a member ID for identifying the member and a file name of the encrypted file from the client apparatus, the encrypted file from the file storage means based on the file name included in the file request, second means for separating the acquired encrypted file into the first encrypted symmetric key portion and the encrypted data portion, third means for transmitting a re-encryption request including the first encrypted symmetric key portion and the member ID included in the file request to the re-encryption apparatus simultaneously with encrypted data transmission processing which is configured to transmit the separated encrypted data portion to the client apparatus, and fourth means for transmitting, upon receiving a second encrypted symmetric key portion obtained by re-encrypting the first encrypted symmetric key portion based on the public key of the member ID from the re-encryption apparatus simultaneously with the encrypted data transmission processing, the second encrypted symmetric key portion to the client apparatus after the encrypted data transmission processing, and the re-encryption apparatus comprising re-encryption key storage means for storing the member ID for identifying the member and a re-encryption key for re-encrypting, without decrypting, the first encrypted symmetric key portion to the second encrypted symmetric key portion in association with each other, means for acquiring, upon receiving the re-encryption request from the file sharing apparatus, the re-encryption key from the re-encryption key storage means based on the member ID included in the re-encryption request, means for re-encrypting the first encrypted symmetric key portion included in the re-encryption request to the second encrypted symmetric key portion based on the acquired re-encryption key, and means for transmitting the second encrypted symmetric key portion obtained by the re-encryption to the file sharing apparatus, wherein the client apparatus is configured to obtain the data by obtaining the symmetric key by decrypting the second encrypted symmetric key portion from the file sharing apparatus based on a private key corresponding to the public key of the member, and decrypting the encrypted data portion from the file sharing apparatus based on the obtained symmetric key. file storage means for storing an encrypted file including a first encrypted symmetric key portion obtained by encrypting a symmetric key based on a public key of the group and an encrypted data portion obtained by encrypting data based on the symmetric key, first means for acquiring, upon receiving a file request including a member ID for identifying the member and a file name of the encrypted file from the client apparatus, the encrypted file from the file storage means based on the file name included in the file request, second means for separating the acquired encrypted file into the first encrypted symmetric key portion and the encrypted data portion, third means for transmitting a re-encryption request including the first encrypted symmetric key portion and the member ID included in the file request to the re-encryption apparatus simultaneously with encrypted data transmission processing which is configured to transmit the separated encrypted data portion to the client apparatus, and fourth means for transmitting, upon receiving a second encrypted symmetric key portion obtained by re-encrypting the first encrypted symmetric key portion based on the public key of the member ID from the re-encryption apparatus simultaneously with the encrypted data transmission processing, the second encrypted symmetric key portion to the client apparatus after the encrypted data transmission processing, and the re-encryption apparatus comprising re-encryption key storage means for storing the member ID for identifying the member and a re-encryption key for re-encrypting, without decrypting, the first encrypted symmetric key portion to the second encrypted symmetric key portion in association with each other, means for acquiring, upon receiving the re-encryption request from the file sharing apparatus, the re-encryption key from the re-encryption key storage means based on the member ID included in the re-encryption request, means for transmitting the second encrypted symmetric key portion obtained by the re-encryption to the file sharing apparatus, wherein the client apparatus is configured to obtain the data by obtaining the symmetric key by decrypting the second encrypted symmetric key portion from the file sharing apparatus based on a private key corresponding to the public key of the member, and decrypting the encrypted data portion from the file sharing apparatus based on the obtained symmetric key.