To decide a user without recording user information in an arithmetic device side, and to allow the use of cookie information and automation of login by a boot by an external medium.

This automatic login authentication system has a step for authenticating the login by uniquely identifying a user ID, an identification number characteristic of the arithmetic device, and authentication data of the external medium 1, having a program reading an operation system; a communication line-connecting program, and a unique identification number the arithmetic device; and an authentication establishment program, by once inputting a passphrase and the ID in an access destination management server 3 by the user by the booting of the arithmetic device 2. The automatic login authentication system also has a step for storing the cookie information transmitted by a WEB server in a memory 11 of the arithmetic device 2, and recording the cookie information of the memory into the management server 3, by an act of cutting a power switch 9 of the arithmetic device 2.