a third preferred embodiment of the digital data storage device in a pen shaped housing in accordance with the present invention includes an upper casing 10 a a bottom casing 11 a a retaining bolt 14 a reservoir tube 12 and a memory device 20 the upper casing 10 a has a bottom opening 103 a and the bottom casing 11 a has a point opening not numbered and a top ring 111 a that is smaller than the bottom opening 103 a of the upper casing 10 a the retaining bolt 14 and the reservoir tube 12 are held in the bottom casing 11 a the memory device 20 with the usb plug is securely mounted in the upper casing 10 a the usb plug 23 faces and protrudes from the bottom opening 103 a the upper casing 10 a and the bottom casing 11 a are joined together by inserting the top ring 111 a into the bottom opening 103 a of the upper casing 10 a when the upper casing 10 a is separated from the bottom casing 11 a the usb plug 23 is exposed and can be inserted into a usb socket not shown in the computer not shown the digital memory device for a computer or other electronic devices with usb socket is in a pen like housing the pen like housing can be carried conveniently and also hold a portable writing instrument.