A product sales processing system includes a portable terminal; a cash register, a customer operating the portable terminal so that product codes are read and stored in the portable terminal, and payment is made at the cash register based on the stored data; and an intermediating device that connects the portable terminal to the cash register such that the portable terminal and the cash register can communicate with each other, the portable terminal comprising: a code reading section that reads the codes that are provided to products; a storage section that stores the codes which have been read by the code reading section; and a communication section that, when the portable terminal is connected to the intermediating device, transmits product purchase information which includes the codes stored in the storage section to the cash register via the intermediating device.