To provide a security system capable of improving a security level by far when compared with a conventional security system.

This security system is composed of exclusive cards 17, 20 and devices 10, 31 protected from the viewpoint of security. The exclusive cards 17, 20 have a tag 21 having an integrated circuit including data for distinguishing a user and an antenna and a polarization filter 19. The devices 10, 31 protected from the viewpoint of security have a reader-writer 23 for reading the data in the tag 21 and a special liquid crystal screen 25 provided with a touch panel part 29 which prevents a user from seeing its liquid crystal screen by the naked eyes during operation and enables the user to see display on the screen through the polarization filter 19. Only when it is found out that the user is the regular user based on the data read by the reader-writer 23, power supply of the special liquid crystal screen 25 is turned on. The user inputs a secret code through the touch panel part 29 of the special liquid crystal screen 25 whose power supply is turned on to operate the devices 10, 31 protected from the viewpoint of security.