A message transmission system comprising: registration accepting means for accepting first communication terminal specifying information specifying a communication terminal, second communication terminal specifying information specifying a communication address of the communication terminal, and subscribed service specifying information specifying a service to which the communication terminal subscribes; subscriber information storing means for storing the first communication terminal specifying information, the second communication terminal specifying information, and the subscribed service specifying information in association with each other; transmission request receiving means for receiving third communication terminal specifying information specifying a communication terminal of a message destination, and provided service specifying information specifying a service provided by a message sender, from a message sender equipment; communication address converting means for referring to the subscriber information storing means on the basis of the third communication terminal specifying information and the provided service specifying information received by the transmission request receiving means, to retrieve the second communication terminal specifying information corresponding to the first communication terminal specifying information agreeing with the third communication terminal specifying information, and the subscribed service specifying information agreeing with the provided service specifying information; and message outputting means for outputting a predetermined message while designating the second communication terminal specifying information retrieved by the communication address converting means, as a communication address. registration accepting means for accepting first communication terminal specifying information specifying a communication terminal, second communication terminal specifying information specifying a communication address of the communication terminal, and subscribed service specifying information specifying a service to which the communication terminal subscribes; subscriber information storing means for storing the first communication terminal specifying information, the second communication terminal specifying information, and the subscribed service specifying information in association with each other; transmission request receiving means for receiving third communication terminal specifying information specifying a communication terminal of a message destination, and provided service specifying information specifying a service provided by a message sender, from a message sender equipment; communication address converting means for referring to the subscriber information storing means on the basis of the third communication terminal specifying information and the provided service specifying information received by the transmission request receiving means, to retrieve the second communication terminal specifying information corresponding to the first communication terminal specifying information agreeing with the third communication terminal specifying information, and the subscribed service specifying information agreeing with the provided service specifying information; and message outputting means for outputting a predetermined message while designating the second communication terminal specifying information retrieved by the communication address converting means, as a communication address.