To allow flexible security level switching according communication situations,
a password holding section holds a plurality of device authentication passwords,
for example, a temporary password and a private password. The temporary password
is valid only under a certain situation and the private password has a high level
of confidentiality to increase the device security. A password management section
allows the user to add a new password to the password holding section and delete
an existing password therefrom. A password selecting section selects the most suitable
password for current connection from among passwords in the password holding section
according to a user event, information acquired by an external factor acquisition
section, and information from a time control section. The selected password is
output to a password checking section.
