A portable information device capable of processing data input from an external device and a method thereof. The portable information device has an interfacing unit in connection with the external device for receiving an input of key data therefrom, and a key code converting unit for converting the input key data into key code values that can be input to the portable information device. As a user can input data through a keypad of a mobile telephone with which he/she is familiar, the user can input data with speed and convenience.