PURPOSE: To obtain a software copy preventing system by calculating a password by a host computer and a black box, when a recognition symbol from the black box has comformed, and collating both passwords.

CONSTITUTION: A recognition symbol is sent from a black box 2, an operational expression in which the recognition symbols becomes an answer of the operational expression as it is prepared, and coincidence of its answer and the recognition symbol is checked. In this case, when sending the recognition symbol, a bar code pen 3a reads the contents displayed by a bar code and uses them as input information, by which it can be inputted to the host 1 as one body with the information. When the bar code information and the recognition symbol are denoted as 123 and A3, respectively, they may be inputted to the host as A3-123. The host checks coincidence of A3, and only when the coincidence has been confirmed, the program is executed.