The invention is embodied, for example, as an electronic cash register (ECR). The ECR is at least provided with numerical keys and a buzzer. When data relating to the prices of goods to be registered is entered with use of the numerical keys, the total sum payable by the customer is calculated and stored in a memory. When a sum received is entered with use of the numerical keys, the sum is similarly stored in the memory. The ECR has a CPU which compares the received sum keyed in with a pattern predetermined based on data relating to the kinds of money in circulation and checks whether the received sum is acceptable relative to the total sum. The buzzer goes on when the received sum is not acceptable.