The beauty of identity-based encryption (IBE) lies in the convenience of public key handling, in the sense that any identification such as an email address, a name, or an IP number can serve as a public key of a party. However, such convenience is not inherited by a system where a party possesses many identities (e.g., many email addresses) and has to use them as his public keys. When this system is handled with astandard IBE, the user must manage all the private keys that are associated with all the public keys (identities). However, keeping these private keys is inconvenient to the user. In this paper, we solve this problem by proposing a novel identity-based encryption where we set a private key that maps multiple public keys (identities); namely, we can use a private key to decrypt multiple ciphertexts; each was encrypted with a different public key (identity).