To obtain a method which allows a neutral observer to store the details of electronic commercial transaction by including a process which aims at fetching and provides recorded communication, etc., and making either of 1st and 2nd parties use a small client technology.

1st and 2nd parties 500 and 502 are illustratively and respectively a client and a server. The N-th party 504 represents a server and probably the server is a server where a user maintains account with which electronic transaction is performed. A neutral observer 100 is connected to communication links 510, 512 and 514 so that the observer 100 can exist within communication paths that connect the parties. And, the transaction parties offer a transaction identifier to the neutral observer. Thus, the neutral observer can identify all of the parties of transaction, automatically extract related transaction details according to a specified protocol and store them.