In a network advertisement system, an information processing section includes a module to store, when sales or service operation is conducted for a first terminal, purchase history of articles or services of the first terminal; and a Social Network Service includes an extraction module to extract, on receiving from the module a notification of the reception of the article or service by the first terminal, registered users related to the user of the first terminal. The SNS notifies the reception of the article or service by the first terminal to terminals of the registered users thus extracted. When a second terminal receives purchase of an article or provision of a service on the basis of the notification of purchase information of plural users, a degree of contribution to the sales promotion is expressed by a numeric value for each of the plural users by referring to the shop server and the SNS to reflect the degree of contribution to the affiliate. Therefore, in the network advertisement system, when a user purchases an article, information of the article is notified to friends of the user to thereby automatically provide an amount of affiliate to the user or a plurality of users.