PURPOSE: To execute discount sales at every merchandise and department.

CONSTITUTION: A merchandise sales data processor 10 processing a sales register based on merchandise data such as a merchandise name and price read in accordance with a merchandise code, etc., is provided with discount rate setting storage means 20 and 13 setting and storing a discount rate at every merchandise or every department to which the merchandise belongs, discriminating means 11 and 12 discriminating whether the discount rate is set and stored or not in the merchandise corresponding to the merchandise code or in the department to which the merchandise belongs and discount sales price deciding means 11 and 12 deciding the sales price of the merchandise whose discount rate is set and stored from a product unit price and the discount rate.