Abstract: An electronic commerce system, which aids in a purchase and a sale of a commodity, allows the purchase or the sale of the commodity at a more desirable price or under a more desirable condition. This system comprises a registered commodity data storing unit storing a desired sale or purchase price of a commodity, and the information about a change condition and a change price of the desired sale or purchase price, and a unit changing the price if the information about the change condition or the change price, which is stored in the registered commodity data storing unit, is satisfied.

Abstract: In the so-called network auction through the internet, in order to support a user's bid and to mitigate a burden in knocking down a desired product, it is known that a reentry is carried out automatically within the maximum frame of bidding price set up by the user, even if the amount of a bid is updated. However, this conventional technology was limited to offering a bid only to single product. So, to solve such a problem, in the present invention, it is made to register the table for predetermined conditions to be matched to two or more products, and by referring to the above-mentioned table, automatically to offer a bid to other products which have a predetermined relation with a certain selected product according to the result of the justice of the closing bid.