To provide a card unauthorized use prevention system, a financial terminal and a host computer of a financial institution, by which the unauthorized use or the like of a user card by a third person can be previously prevented.

The card unauthorized use prevention system S is constituted of a card C, a portable telephone 1, a financial terminal 4 installed in a store 3, and a host computer 50 in a financial institution 5. The host computer 50 receives the portable telephone number information and password information of the card C, financial transaction information with a card user 10 and the store information of the store 3, which are transmitted from the financial terminal 4. When the positional information of the portable telephone 1 is not registered in a base station BS1 near to the seat of the financial terminal 4, the host computer 50 informs the financial terminal 4 of the impossibility of financial transactions. When the financial terminal 4 receives the information of financial transaction impossibility from the host computer 50, the financial terminal 4 displays impossibility of financial transactions.