A protection device comprises a substrate, a fusible element, a flux and an insulating cover. The fusible element is disposed on the substrate and connects to a power line of an apparatus to be protected. The flux is disposed on the fusible element. The insulating cover is secured on the substrate to form a room for receiving the fusible element. The insulating cover has a bottom surface facing the substrate, and a plurality of protrusions are formed and distributed on the bottom surface to hold the flux in place.