Provided are a protection circuit and a photovoltaic system capable of irreversibly interrupting a current path of photovoltaic units such as solar cells by a signal in an emergency such as a fire. The protection circuit includes: a photovoltaic units 26, a protection element 2 provided on a current path of the photovoltaic units 26, and a switch 3 for activating the protection element 2, wherein the protection element 2 irreversibly interrupts the current path of the photovoltaic units 26.