(57) A plurality of means for inputting digits of a password number are adapted to be manually operated. A means is provided for displaying the mapping between each of the plurality of digit inputting means and the digit which it currently represents and inputs when actuated, and also there is provided a means for altering this mapping. The altering means alters the mapping between the digit inputting means and the digits which they represents and input when actuated, every time a password number is inputted. Thereby, if an evilly intentioned person should watch a user actuating the digit inputting means, he will not be able to discern the user's password number by observing his finger movements. Optionally, a means is provided for restricting the visibility of the means for displaying the mapping between each of the plurality of digit inputting means and the digit which is currently represents to within a relatively narrow solid angle, so as to make peeking more difficult.