PURPOSE: To perform fermentation improved economically effectively, by installing, on an automobile, a fermenting tank having feed ports, a discharge port and suitable volume to contg. fermentation germs such as Bacillus naijo, Bacillus natto and materials to be treated.

CONSTITUTION: After plural kinds of microbes such as Bacillus natto, Bacillus naijo or the like are beforehand charged into a fermenting tank 2, materials to be treated such as screened crude refuge, poultry dung, sludge or the like are charged through the 1st feed port or the 2nd feed port 5 into the tank 2. The temp. and conc. in the tank 2 are monitored with a monitoring device and respective ventilation fans 11 and ventilation ports 12, 13, 14 are operated to suck or discharge air, whereby the environment suited for growth and alteration of aerobic germs and anaerobic germs is created to maintain the inside of the tank to be the suitable state for fermentation of the materials to be treated by the effect of the Bacillus naijo and to accelerate the fermentation.