To achieve both information confidentiality management and early discovery of information leak.A file encrypting/decrypting program makes a computer execute a process including a step of creating a session key (a1); a step of encrypting a file (f1) with the key (a1), thereby creating a file (f2); a step of encrypting the key (a1) with a public key (b1), thereby creating a key (a2); a step of encrypting the key (a1) with a public key (c1), thereby creating a key (a3); and a step of creating a combined file (f3) including the file (f2) and the keys (a2, a3); and a process including a step of separating the file(f3) into the file (f2) and the keys (a2, a3); a decrypting step of decrypting the file (f2) into the file (f1) with the key (a1); a step of decrypting the key (a2) into the key (a1) with a private key (b2) corresponding to the key (b1) and then proceeding to the decrypting step; and a step of decrypting the key (a3) into the key (a1) with a private key (c2) corresponding to the key (c1) and then proceeding to the decrypting step.