PURPOSE: To efficiently execute unit price changing at the discount sale of goods by executing the unit price changing to a discount unit price included in discount data when it is discriminated by a discount sale discriminating means that the discount sale is executed.

CONSTITUTION: Discount data which consists of a discount starting point number and a discount price defined in advance are stored by a goods code by discount data storing means 10a4 and 10a5. When the goods code is inputted by an input means at the registering of sales goods, it is discriminated by a discount sale discriminating means whether discount sale is executed or not based on comparison between a point included in goods data corresponding to the goods code among the goods data stored by goods data storing means 10a1 to 10a3, 10a7 and 10a8 and the discount starting point included in the discount data corresponding to the goods code among the discount data stored in the discount data storing means 10a4 and 10a5. Then, when it is discriminated that the discount sale is executed, unit price changing to a discount unit price included in the discount data is executed by a unit price changing means. Thus, discount sales service to customers is executed efficiently.