To provide order information transmitting technology which effectively uses a portable telephone set since a personal computer is required for the electronic trade transaction of a product and service and the personal computer is large, expensive and it lacks portability.

The product of a purchase object and service are decided by viewing the screen of a sales terminal machine 10. When the portable telephone set 10 is installed on a sales terminal machine 20B and information (an order item, a telephone number and electronic money information or the like) are transmitted, information are transmitted to a sales data center 30 from the sales terminal machine 20B and order recognition information is transmitted to the sales data center 30 to the portable telephone set 10.