A method of transmitting email and a device for transmitting email capable of broadcasting the email including encrypted data effectively. When a personal computer PC1 accepts an instruction to transmit same data to multiple destinations by email, the PC1 generates a session key (S105) and encrypts the data by utilizing the generated session key (S106). Next, the PC1 generates the common key by utilizing a public key generated based on an email address of each destination and the secret key acquired from a center in advance (S107), and encrypts the session key by utilizing the generated common key (S108). The PC1 transmits the email including the encrypted data and the encrypted session key to each destination (S110).