A password input device comprises a storage unit for storing character strings according to each icon; an input window generation unit for generating and displaying an input window on which a plurality of icons are arranged; a secret icon recognition unit which confirms a shift coordinate value and recognizes icons, which are arranged on coordinates inversely moved up to the shift coordinate value from a coordinate value at which a selected icon is arranged, as secret icons selected by the user if the user selects the icon; and an authentication processing unit which confirms a character string corresponding to each secret icon recognized in the secret icon recognition unit, generates a combined character string in which the one or more confirmed character strings are arranged, and authenticates the user by confirming whether the generated combined character string is consistent with the user's password stored in the storage unit.