A method of certifying the existence of electronic information released on a network at a time and date. The network connects one or more computer servers and a plurality of client computers with each other. Electronic information of a web page stored in one of the plurality of client computers is accessed using information of its location from one of the computer servers based on a request from one of the client computers. A copy of the electronic information is then obtained. Attribute information is generated from the location, access time, and date when the electronic information is accessed. An electronic certificate may be generated by uniquely specifying the electronic information and the attribute information as inherent information identifying the electronic information. The copy of the electronic information is stored in a memory by tying up the electronic information with the electronic certificate and the attribute information. At least the electronic certificate, the attribute information, and preferably the copy of the electronic information can also be read and provided from the memory to the one of the client computers or its operator as a requester.