There are provided a radio communication terminal device and a radio communication function control method enabling a user to perform off-operation of only the mobile telephone function when the user is in a radio LAN area. In the device and the method, a radio dual terminal (100) is a radio communication terminal device having both of the communication function via a mobile telephone base station (101) of a mobile telephone system (mobile telephone function) and the communication function via a radio LAN base station (102) of the radio LAN system (radio LAN function). When the radio dual terminal (100) comes into the radio LAN area (104), a message asking whether to turn off the mobile telephone function appears on the display screen. If the user answers Yes, only the mobile telephone function is turned off, thereby reducing the power consumption when in the radio LAN area (104). It should be noted that when the radio dual terminal (100) goes out of the radio LAN area (104), the mobile telephone function which has been off is automatically turned on.