PURPOSE: To promote sale by detecting the serial transaction number of one transaction in a adjustment process after sold articles are registered, automatically judging whether or not there is a privilege in the transaction, and eliminating a trouble time and improving the certainty.

CONSTITUTION: Transaction serial numbers and corresponding discount rates are set previously in a special reduction table 27 before a stored is opened. After the store is opened, sale registration is performed by exactly the same key operation as before and each customer is given a serial transaction number. When this serial number matches with a number set in the table 27, the total amount of money of the customer is automatically discounted. Thus, the privilege like lottery is given by using the serial transaction numbers, and the sale is promoted consequently. Further, neither clerks nor customers need not confirm the transaction numbers on issued receipts, so the trouble is eliminated and the privilege can securely be given.