A portable terminal device in which a preset input mode can be forcibly return to by a simple operation and the user convenience and operability can be improved and its input mode control method. When the operation of a specific key is detected or the operating time of the specific key is monitored and it is detected that the specific key is continuously operated for a predetermined time or more, a control unit 16 forcibly returns the mode to the preset input mode and displays input characters or symbols in a preset language or language effective in the area to which the terminal device belongs.