PURPOSE: To prevent that a password leaks in an unfair way by providing a password correct/error decision deciding means, a penalty calculating means and a password input request means.

CONSTITUTION: A password correct/error decision deciding means 2 has a means 3 to count and store the frequency to input erroneously a password and a means 4 to count and store the number of erroneous characters in the inputted password. A penalty calculating means 5 calculates a penalty P which increases as the input frequency and the number of the erroneous characters increase and decreases by the input of the correct password, and an input request means 7 requests the inputting person to input the correct password until the penalty P becomes zero. Thus, it can be prevented that the password in an unfair way leaks, and even when the above person to know the correct password repeats the simple input error, the input of the correct password does not become impossible and on the other hand, the possibility that an evil-minded third person not knowing the correct password can appropriate the correct password is lowered.