PURPOSE: To make a computer applied equipment compact, to reduce cost and to provide the data storage device which improves performance corresponding to comparatively higher price.

CONSTITUTION: This data storage device externally attached to the computer applied equipment is provided with an IC card type connection adapter 3 and a data storage means 2 provided in inside a case 1, and the IC card type connection adapter 3 is connected to a slot for IC card provided at the computer applied equipment so as to connect the data storage means 2 to the computer applied equipment. Further, the IC card type connection adapter 3 incorporates an IC memory 8 at least, can be attached and detached to the enclosure 1 and is added a function for enabling independent use as the IC card.