To prevent the investment from being more than the preset loss by obtaining the information of a transaction market and ordering the transaction by means of a computer through a communication network and starting the liquidation of the transaction when a liquidation decision value having the change speed and the change acceleration of a transaction price as a variable becomes lower than a threshold.

A computer 1 to be used by a user is connected to the transaction market 2 and a transaction intermediary 3 through a network 4, and a financial organ 5 for receiving/paying price is set. Then, market price information 11 is received from the market 2 and a transaction order 12 is outputted to the intermediary 3 by the computer 1 of the user. A transaction trader executes the transaction in the transaction market. In this case, the liquidation is started in the case of danger that total equity exceeds the preset lower limit threshold (for example, lower than the principal). When liquidation is executed, individual investing object whose liquidation decision value Xi is positive is excluded from a liquidating object to preferentially liquidate the investing object whose Xi is negative.