To provide a program or a device for commercial transactions of building materials and a commercial transaction system for the building materials for dissolving anxiety of credit management and without requiring many layers of routes.

A seller 3 performs credit enquiry to a banking facility 5 according to an order from an orderer 4, the transaction is established when costs can be collected even when the transaction is performed as a result of the enquiry of the credit and the seller 3 arranges ordered articles and delivers them to the orderer. Together with that, the seller 3 claims sales to the banking facility 5 and receives settlement of the costs from the banking facility 5. Since the credit enquiry is performed beforehand to the settlement of the costs, the program or the device for commercial transaction of the building materials and the commercial transaction system for the building materials without causing credit anxiety are provided.