A coupling mechanism for coupling an electronic device to an outer casing includes a plurality of hook-shaped brackets interposed between a front cover and a rear cover of the electronic device, where the plurality of hook-shaped brackets pass through an accommodation hole of the outer casing and are held to hook the outer casing while the front cover and the rear cover are coupled to each other; a plurality of main bracket-mounted portions defined in the front cover, where each of the plurality of hook-shaped brackets is mounted into each of the plurality of main bracket-mounted portions; and a plurality of auxiliary bracket-mounted portions disposed on the rear cover, where each of the plurality of auxiliary bracket-mounted portions is engaged with each of the plurality of hook-shaped brackets when the front cover and the rear cover are coupled to each other.