To provide a method for transferring telephone book data capable of simply and efficiently realizing the transmission and reception of telephone book data and improving convenience.

This method for transferring telephone book data capable of transferring telephone book data through an electronic mail by using a communication terminal device for transmitting and receiving data through the Internet comprises a transmission step S1 for assigning ID numbers to the respective items of the telephone book data stored in the communication terminal device, a transmission step S2 for converting the telephone book data into a data string for transfer in a specific data format including the ID number, a transmission step S3 for forming a file for transfer by setting a unique character string indicating the transfer of the telephone book data at the head of the data string for transfer, a transmission step S4 for setting the file for transfer as an E mail, and a transmission step S5 for transmitting the E mail.