PROTECTING DEVICE AND BATTERY PACK

To provide a protecting device and a battery pack using the same, which are less likely to cause a spark even when a high voltage is applied and can safely and quickly interrupt the current path. A protecting device includes: an insulating substrate ; a fuse element ; a heat-generator which generates heat to blow the fuse element ; a heat-generator feeding electrode which serves as a power-feeding terminal to the heat-generator ; an insulating layer which covers the heat-generator ; and a heat-generator lead-out electrode which is formed along the heat-generator on the insulating layer and holds the melted conductor of the fuse element , wherein, when the heat-generator is energized, the heat-generator feeding electrode side thereof works as a high potential portion and the heat-generator lead-out electrode side thereof works as a low potential portion, and in the heat-generator lead-out electrode , an overlapping area in which a distal end portion extending in the high potential portion side of the heat-generator overlaps the heat-generator is smaller than an overlapping area in which a proximal end portion extending in the low potential portion side of heat-generator overlaps the heat-generator