PURPOSE: To prevent the settlement of account from being executed in the transaction of the same commodity by the two kinds of sales prices by providing a comparing means to compare a transaction starting time and a changed time in the commodity fluctuation information of a commodity code.

CONSTITUTION: When the date and time to start the transaction are obtained from a time mechanism 14 and the commodity code, etc., is inputted from an input device 11, a commodity information judgement part 15 retrieves the commodity information from a commodity information file 12 and compares the transaction starting date and time, which are obtained in advance, with the changed date and time of these commodity information. In the case of transaction starting date and time ≥ commodity information changed date and time, the newest information of the commodity fluctuation information in the commodity information file 12 is adopted and in the case of the transaction starting date and time < commodity information changed date and time, the preceding information are adopted. Thus, even when a customer buys plural commodities and the sales price of the commodity is changed during the transaction of the commodity, only the same sales price is outputted on a receipt.