A waterproof key apparatus, as an electronic device, is provided. The waterproof key apparatus includes a main case, a key module attached to a side of the main case and comprises a key actuator, a window to which the key module is coupled, a universal serial bus (USB) coupling module and a printed circuit board (PCB) attached to an opposite side of the main case, with a dome sheet therebetween, a key bracket and an antenna cap coupled to the lower portion of the PCB, and a sealing part attached between the main case and the PCB to seal the rear surface of the PCB.