An information device security management method which can limit access to certain information by use of fingerprint authentication, the security management method comprising: performing fingerprint authentication if fingerprint authentication is successful within a predetermined number of times, permitting access to said certain information, and, if fingerprint authentication fails for a predetermined number of times, enabling PIN code authentication; after the fingerprint authentication is switched to PIN code authentication, performing PIN code authentication if PIN code authentication is successful within a predetermined number of times, permitting access to said certain information, and, if PIN code authentication fails for a predetermined number of times, enabling an authentication failure flag such that only authentication by means of fingerprint authentication can be performed, and a power source is turned off forcibly as a defensive state, and only fingerprint authentication is performed when the power source is turned on again, no matter how many times fingerprint authentication fails; and thereafter, upon successful fingerprint authentication, disabling the authentication failure flag so that the process returns to the said fingerprint authentication stage; wherein the number of failure times of PIN code authentication is stored in a non-volatile manner, and, if the power source is turned off before the number of PIN code authentication times reaches a predetermined number and then the power source is turned on again, the number of failure times of PIN code authentication is counted with the stored number of failure times serving as the initial value, so as to limit the predetermined allowed number of failure times of PIN code authentication even if the power source is turned on again; and the number of failure times of fingerprint authentication is stored in a volatile manner, and the number of failure times of fingerprint authentication is cleared on switching to PIN-code authentication. performing fingerprint authentication if fingerprint authentication is successful within a predetermined number of times, permitting access to said certain information, and, if fingerprint authentication fails for a predetermined number of times, enabling PIN code authentication; after the fingerprint authentication is switched to PIN code authentication, performing PIN code authentication if PIN code authentication is successful within a predetermined number of times, permitting access to said certain information, and, if PIN code authentication fails for a predetermined number of times, enabling an authentication failure flag such that only authentication by means of fingerprint authentication can be performed, and a power source is turned off forcibly as a defensive state, and only fingerprint authentication is performed when the power source is turned on again, no matter how many times fingerprint authentication fails; and thereafter, upon successful fingerprint authentication, disabling the authentication failure flag so that the process returns to the said fingerprint authentication stage; wherein the number of failure times of PIN code authentication is stored in a non-volatile manner, and, if the power source is turned off before the number of PIN code authentication times reaches a predetermined number and then the power source is turned on again, the number of failure times of PIN code authentication is counted with the stored number of failure times serving as the initial value, so as to limit the predetermined allowed number of failure times of PIN code authentication even if the power source is turned on again; and the number of failure times of fingerprint authentication is stored in a volatile manner, and the number of failure times of fingerprint authentication is cleared on switching to PIN-code authentication.