PURPOSE: To obtain a commodity sales data processor which can prevent the paying mistakes of change by using a prescribed storage means, the sheet number calculation means which calculate the sheet number based on a payment pattern, a total weight calculation means, and the report means.

CONSTITUTION: A commodity sales data processor which inputs the weight data measured by a balance 25 contains a storage means 14 which stores the unit weight for each type of cash, the sheet number calculation means 11 and 13 which calculate the sheet number of each type of cash from the change amount based on a payment pattern set previously, the total weight calculation means 11 and 13 which calculate the total weight of the change amount from the sheets numbers of each type of cash calculated by the sheet number calculation means and the unit weight of each type of cash stored in the means 14, and the report means 11 and 13 which compare the total weight calculated by the total weight calculation means with the weight data given from the balance 25 and report the coincidence or the discordance of comparison. In such a constitution, an operator can confirm whether the change to be payed is correct or not from the reported result. Thus the paying mistakes of change can be eliminated.