A message transfer system 3 is provided with a transmission request receiver 301 for receiving transmission request information containing a membership number being destination information, and message data, from a Web server 2b or from a communication terminal 2a; a message converter 306 for converting the message data into transmitting message data in a predetermined format; a message output part 308 for adding communication address information corresponding to the membership number, to the transmitting message data and outputting the resultant; and a restricted data detector 305 for, when detecting predetermined restricted object data in the message data in the transmission request information, performing a control not to transmit the restricted object data.