PURPOSE: To secure the safety of a computer network system and to improve the operability.

CONSTITUTION: A user perform the input (100) of a user name to a computer to be used. The computer sends the inputted user name and requests (101) the identity confirmation of the user. A computer for user information control investigates (102) whether or not the user name is registered, and when the user name is registered, a key (initializing key) for cirtification is made (103), the key is encoded by the password of the user to whom the identity confirmation is requested, and returned (104) as an initial ticket. The computer, when the password is inputted (106) from the user, decodes (107) the initial ticket sent from the certifying service part by the password, permits the use of the user, and when the decoding cannot be performed, the use of the user is not permitted.