Protective element and battery pack

Provided are a protective element and a battery pack that maintain current capacity at the time of overcurrent protection and that use heat emitted by a heating element to reliably cause melting. The protective element is provided with: a first insulating substrate (55); first and second external electrodes (51, 52); a heating element (57) that is provided to the rear surface (55b) side of the first insulating substrate (55); front/rear surface electrodes (56, 64) that are provided between the first external electrode (51) and the second external electrode (52) of the surface (55a) of the first insulating substrate (55); a meltable conductor (53) that is layered across the first and second external electrodes (51, 52) so as to overlap with the surface electrode (56) on the front surface (55a); a through hole (58) comprising a conductive layer (65) on the inner surface thereof; and a preliminary solder (66) that is used to fill the interior of the through hole (58). The heat of the heating element (57) causes the preliminary solder (66) and the meltable conductor (53) to melt. The wettability of the front/rear surface electrodes (56, 64), the conductor layer (65) that is within the through hole (58), and the like causes the melted preliminary solder (66) and the meltable conductor (53) to move to the rear surface (55b) side of the high-temperature first insulating substrate (55).