PURPOSE: To set a user free from managing many secret keys when all user groups having the same reference right for each information are set by securing the correspondence between the user groups and the coding incidental information obtained by coding the coding key of the information by the secret key of the user.

CONSTITUTION: An information provider codes the offering information by a certain coding key and generates the coding information (S1). Then the coding key is coded by means of a secret key that is shared by the information provider and a user who has the reference right to the offered information (S2). The secret key is stored in a data base together with the coding information as the coding incidental information (S3). In a reference mode, a user of a user group having the reference right acquires the coding information and the coding incidental information from the data base. Then the user decodes the coding incidental information by the secret key in order to calculate a coding key (S4) and then decodes the coding information by the coding key to obtain the offered information. Therefore the user has not to manage many secret keys.