Abstract: A flexible joint purchase order system in which a sales price is determined based on demand without causing a seller to have a loss, comprising: an accepting means for accepting purchase application information and reporting an application for purchase, an entry price of an article, and a desired quantity; an order data table for storing the application for purchase, the entry price, and the desired quantity; a condition table for registering an initial cost, a fixed cost, and a maximum sales quantity; and a network for comparing a first value (equal to the entry price times the desired quantity of articles entered at prices equal to or higher than the entry price) with a second value (equal to the initial cost added to the product of the fixed cost and the desired quantity), for determining the sales to be made, and for transmitting the entry price as the sales-determined price.