To realize a POS system capable of simplifying the cash handling work upon alternation of an operator.

This POS system uses a paying and receiving method wherein coins of the change given to a customer are paid from an automatic change machine 7, bank notes are taken out of a drawer 6, the bank notes for deposits received from the customer are stored to the drawer 6 and the coins are stored in the automatic change machine 7. The POS system can perform the commodity registration, calculates the total amount of money for purchase, calculates the amount of change from the input deposits received and totals the cash sales as theoretical cash stock. The POS system is provided with a first cash stock reading means for reading the cash stock amount of the automatic change machine 7 upon opening operation for enabling the operation, a second cash stock reading means for reading cash stock amount of the automatic change machine 7 upon closing operation for prohibiting the operation, and an adjusting means for adjusting the theoretical cash stock by the change portion between the cash stock by means of the first cash stock reading means and the cash stock by means of the second cash stock reading means.