A terminal device such as a mobile terminal is provided with two real-time clocks
which are powered by different power sources: a first real-time clock which is
built in a control section (built-in microcomputer 1, for example) of the
terminal device; and a second real-time clock which is provided outside the control
section. At power-on of the mobile terminal or on recovery from failure such as
a power cut, clock/calendar information is read out from the second real-time clock
and is set to the first real-time clock, and thereafter, the control section obtains
the clock/calendar information from the first real-time clock. The second real-time
clock is connected to the control section directly by a signal line or via a functional
device, or the second real-time clock is built in a functional device which is
connected to the control section. By such composition and operation, the clock/calendar
information can be maintained reliably and correctly even if failure occurred to
the control section. The readout of the clock/calendar information is carried out
usually from the first real-time clock (built-in RTC), therefore, high readout
speed can be realized.