a housing which constitutes an outer shell of a main body having a shielding property against electronic radiation and an opening provided on a bottom wall, said opening is smaller than the total mounting area of a plurality of extension modules that are layered each other;

a motherboard installed in the housing;

a stud attached on the bottom surface of the motherboard and co-fastening the plurality of extension modules with one set of screws; and

a lid which has a shielding property against electromagnetic radiation and which covers the opening, wherein

the plurality of extension modules includes a modem daughter card module with modem functions and a subscriber identity module mounted module on which a subscriber identity module card is mounted, and the extension module are mounted on the motherboard by any one of at least three forms of:

fixing the modem daughter card module in a single layer to the stud;

fixing the subscriber identity module-mounted module in a single layer to the stud; and

fixing the modem daughter card module and the subscriber identity module-mounted module to the stud by piling each other with spacer therebetween disposing the modem daughter card module close to the motherboard.