a product - selling - data processing apparatus which performs a bundle - of - selling in which a predetermined number of a same kind of articles each having a unit price are sold in a lump at a price lower than the total of the unit price of the predetermined number of the articles , includes an article code inputting device for inputting a first article code identifying an article to be sold , a memory for memorizing price data including the unit price of the articles and a bundle - of - selling price of the articles , and article code data including the first article code and a second article code identifying an article to be sold as a bundle - of - selling , the second article code being modified based on the first article code , the price data being memorized in correspondence with the article code data , a discerning device for discerning whether the article indicated the first article code inputted by the article code inputting device , can be sold as the bundle - of - selling , a first calculation device for calculating selling data based on the bundle - of - selling price specified by the second article code which corresponds to the first article code when the first article code is inputted by the article code inputting device and the bundle - of - selling is carried out , a first memory control device for memorizing the selling data calculated by the first calculation device in the memory device .