An object of the present invention is to, in settlement by electronic money, reduce burden on an electronic money server and enhance convenience for users. The function of generating transaction numbers is transferred from the electronic money server to affiliated store servers, so that the transaction numbers are generated by the affiliated store servers. The transaction numbers are each associated with transaction information calculated in accordance with a calculation rule confidential to third parties, such that the electronic money server can detect the presence of alteration of the transaction information based on the transaction number. Furthermore, at the time of generating a transaction number, a seed, which is time-limited secret information confidential to third parties, is inputted to the calculation rule along with the transaction information and used for calculating the transaction number, whereby it is possible to further enhance the level of security.