Abstract: An external expansion apparatus for a portable computer is provided. The expansion apparatus is detachably connected via a cable to the portable computer for providing functional expansion for the portable computer when connected to the portable computer. The expansion apparatus includes a box body having a plurality of accommodating rooms. Each of the plurality of the rooms is for accommodating one of detachable expansion units of different types. The expansion apparatus also includes a communication control circuit for controlling the communication between the portable computer. In particular, because each of the plurality of expansion units is formed a module, the expansion apparatus can provides users with multiple choices and a great degree of convenience for the functional expansion of the portable computer. In the invention, one of the inserted expansion units can be a data storage device, or a modem, or an optical-disk drive device, etc.