To obtain a means for classifying a set of information contents to be previously provided to an information damander into one or plural classes and stepwisely disclosing the contents to the demander.

In the information providing service system to be executed through a computer network 17, an information demander's computer 10 has an input means 11 for reading out provided information, a preprocessing means 12 for executing preprocessing to receive an unlocking key for information ciphered by an electronic key from an information provider, an unlocking key request means 13 for requesting the unlocking key to an information provider's computer 15, and a decoding means 14 for receiving the unlocking key and decoding the ciphered information by the unlocking key. The computer 15 has an unlocking key distributing means 16 for checking a prescribed condition for the unlocking key request from the computer 10 and then distributing the unlocking key to the computer 10.