A system and method which support securities transactions, preventing the market price from fluctuating when introducing a new set of securities to the public. In this trade support system, a trade processing unit processes buying and selling orders received online from customers' terminals. Each time a deal is completed, the trade price acquisition unit takes in the resultant trade price. A price evaluation unit determines whether the acquired trade price meets the offering price that is suggested in the prospectus of the public offering. If the former is lower than the latter, the price evaluation unit so notifies a trading order placement unit. A subscription period checking unit, on the other hand, checks whether the present date and time is within the subscription period. The trading order placement unit places a buying or selling order at a price within an allowable range around the suggested offering price, when an excessive difference between the trade price and suggested offering price is found during the subscription period. As a result of the above operation, the market price is stabilized during the subscription period.