With the spread of photovoltaic power generating systems for houses, the fire cases caused by a malfunction of the apparatus increase. However, the fire detection means of the photovoltaic power generating system is not installed at present. In addition, there is little knowledge about the fire of the photovoltaic module. Therefore we performed the experiment that assumed the fire of the photovoltaic module installed on the house roof and we observed the combustion condition of the photovoltaic module. As a result of the experiment, we confirmed that combustion spreads toward the upward photovoltaic module along the roof by combustion on the back side of the photovoltaic module. We examined a fire detection line installed on the back side of the photovoltaic module as a fire detection method according to this laboratory finding. We confirmed the effectiveness of the fire detection on the back of the photovoltaic module by performing the fire experiment assumed that a photovoltaic power generating system for houses of 1.25kW using six pieces of photovoltaic modules with the maximum power of 208W and by installing the fire detection line at the upper part of the back side of the photovoltaic module.