A hand-held electronic device comprises an IC-card chip unit, a watch CPU, a power source unit, a display unit, and a switch connected between the power source unit and the IC-card chip unit. The watch CPU has a power supply controlling unit. The IC-card chip unit performs contactless data communication with an external transmitter-receiver in close range. The watch CPU operates on power from the power source unit, receives data from the IC-card chip unit to display the data on the display unit or to process the data before displaying them on the display unit. The power supply controlling unit closes a switch at least during the period of time that the watch CPU receives data from the IC-card chip unit, thereby causing power to be supplied from the power source unit to the IC-card chip unit.