A mobile digital device comprises a ten-key pad being comprised of a key mat 21 on which ten-key buttons 21a-21c with respective projections 21aa-21cc on the under surfaces thereof are laid out and a key circuit board on which respective contacts 22a-22c corresponding to the projections are laid out, an electrostatic capacity sensing pad 30 for sensing an electrostatic capacity change to detect a touched region and having through holes to be inserted the projections corresponding thereto and being provided with between the key mat 21 and the key circuit board 22, and a controller for selecting a function corresponded to a feature of the touched region detected by the electrostatic capacity sensing pad and executing the selected function. Owing to such constructions, a desired function can be selected by way of finger touching to the mobile digital device.