Abstract: The present invention provides a commercial transaction system which enables goods to be sold and bought with high accuracy without anxiety by using a computer network such as the Internet, and which can also give credit information in commercial transaction. The electronic commercial transaction system according to the invention includes plural electronic terminals connected to one another by a computer network, and an authentication station connected to the computer network. An electronic certificate and a company code are assigned to each of the electronic terminals on the basis of examination performed by the authentication station, and when a commercial transaction is to be performed between one and another of the electronic terminals via the computer network, both selling and buying sides of the commercial transaction present the respective electronic certificates before performing the commercial transaction.