A decryption apparatus stores secret keys, each of which is specified by two nodes in tree structure in first memory, one of the two nodes indicated by ciphertext index information item of the decryptable ciphertext being an ancestor node of leaf and the other of the two nodes being a node which is not an ancestor node of leaf, and stores an identifier of decryption apparatus corresponding to a leaf in a tree structure in a second memory. The decryption apparatus acquires a plurality of ciphertexts, each ciphertext including a ciphertext index information item indicating two nodes in the tree structure which correspond to a decryption key for decrypting the respective ciphertext, and acquires a decryptable ciphertext from the plurality of ciphertexts. Further, the decryption apparatus selects, from the stored secret keys, a secret key corresponding to the respective ciphertext, and derives a decryption key from the selected secret key to decrypt the decryptable ciphertext by using the derived decryption key.