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 agent substitute registers advertising service substitution conditions, whereby when the advertisement requester and the advertising agent substitute come to an agreement based on the advertising service substitution conditions and the advertisement request conditions so registered, the advertisement requester pays part of or the whole of expenditures for an advertising material and advertisement using the same, whereas the advertising agent substitute executes an advertisement on behalf of the advertisement requester by wearing, using, displaying, selling, lending or distributing the advertising material.