To provide a method for producing methane gas and a fermentation product, using an anaerobic bacterium methane gas fermentation apparatus and an aerobic bacterium fermentation apparatus, and performing the effective utilization of biological heat and the deodorizing treatment of a waste fluid to stably and safely produce the methane gas and the fermentation product at low costs, and to provide an apparatus for producing the methane gas and the fermentation product.

This method for producing the methane gas and the fermentation product, using an anaerobic bacterium methane gas fermentation apparatus [A] and an aerobic bacterium fermentation apparatus [B] using an aerobic high temperature bacterium having the optimal activity temperature of ≥80°C or its bacterium mixture or their culture product, is characterized by heating the exhaust heat with the effective means of a heat pump 20 to use the heat for heating ventilation air or a methane gas raw material, thus promoting the fermentation.