Abstract: An advertising media information mediating system is provided which uses a computer system for providing an advertising service substitution method and in which an advertisement requester can register advertisement request conditions on an advertising media information mediating server through a simple operation, whereas an advertising agent substitute, who executes an advertisement on behalf of the advertisement requester, can register advertising service substitution conditions on the advertising media information mediating server through a simple operation, whereby the advertisement requester and the advertising agent substitute can select an advertising transaction partner which can meet conditions desired by the advertisement requester and the advertising agent substitute from a variety of selection targets via a network without spending much time, the advertising service substitution method being such that the advertisement requester registers advertisement request conditions, whereas the advertising ag