12. A system according to claim 10, wherein when the message is posted, said server adds an identification code to a quotation sentence which cites said posted message, posts the message into said database, and specifies a duplicated portion of the message from said series of messages by using said identification code.
10. An electronic message system in which a plurality of users can post messages and the user refers to the posted messages, comprising: a client for transmitting a message or a request from the user; and a server for processing the message or request transmitted from said client through a network, wherein said server comprises a database which registers a plurality of kinds of message types which have previously been defined, a message inputted to said client, and a posted message in a case where said message is a message according to said posted message, and summary forming means which merges a plurality of specified related messages on a basis of information for related subject of said message types and each of the posted messages and which forms a summary by leaving at least one duplicated message among duplicated portions where the messages continue among the series of merged messages and by deleting others.