To enable only user who passes personal authentication to perform business trade by performing the personal authentication by using a device whose place of use is not restricted like a multimedia portable terminal and by combination of information which is unique to an individual and impossible to be forged like a retina pattern and a fingerprint.

The business trade is performed by making access from the multimedia portable terminal 1 to a store 17 by a user, their own bank account numbers are ciphered so as not to be known to the opposite party, added to a trade result, transmitted to the opposite party of the trade by both of the user and the store, own ciphered keys each is added to the information transmitted from the opposite party and the information is transmitted to a bank 7 by each of the user and the store. The trading result of the information transmitted from both of the user and the store are deciphered by using a ciphering key attached by each party of the trade, coincidence of a purchasing amount of the trade transmitted by the user with a sale amount transmitted by the store is confirmed and the amount is transferred from the bank account only when the amounts coincide with each other by the bank.