Clock signal switching device of an IC Card

When an IC card (1) is attached to a terminal unit (30), a counter (17) counts pulses of an external clock signal and a switching circuit (20) outputs the external clock signal to an internal circuit (5) in place of an internal clock signal if a NAND gate (18) determines that the count of pulses of the external clock signal by the counter (17) is a predetermined value. When the IC card is ejected from the terminal unit, pulses of the internal clock signal are counted by a counter (7) and when the count attains a predetermined value, the counter (17) is cleared and the switching circuit outputs the internal clock signal to the internal circuit in place of the external clock signal in response to the output of the NAND gate (18). Thus, it can be correctly determined whether the IC card is operated in the form of a single body or in the form attached to any terminal unit.