A portion-to-be-melted of a fuse is surrounded by plates, so that heat to be generated in a meltdown portion of the fuse under current supply can be confined or accumulated in the vicinity of the meltdown portion of the fuse. This makes it possible to facilitate meltdown of the fuse. The meltdown portion of the fuse in a folded form, rather than in a single here a fuse composed of a straight-line form, is more successful in readily concentrating the heat generated in the fuse under current supply into the meltdown portion, and in further facilitating the meltdown of the fuse.