TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred System: The system comprises a magnet which is attached to the support of the stirring blade, stirring shaft, scrubber apparatus from which solid components contained in methane gas including sludge and scum are removed, supply tank (6) which stores temporarily the solution containing the organic acid for interposing between the acid production tank and methane fermentation tank, liquid feeding pump which feeds the solution for supplying the methane fermentation tank towards the methane fermentation tank from the supply tank, first float switch which outputs the signal which starts the liquid feeding pump when it raises to the predetermined liquid level with the first liquid level of the supply tank, where second predetermined liquid level of the supply tank is lower than the first predetermined liquid level, second float switch which outputs the signal which stops the liquid feeding pump, space of first float switch and second float switch which is adjusted such that the intermittent stop period when the liquid feeding pump is stopped intermittently is below setting value, and a flow meter which measures inflow of the solution which flows into the supply tank from the acid production tank. The system further comprises an inverter control unit which drives the liquid feeding pump based on the inverter frequency determined from the inflow of the solution measured by the flow meter, drum which has a discharge port for discharging insertion opening into which the organic waste accommodated in the wrapping material are thrown, and fractionates wrapping material outside, rotating shaft penetrated and rotationally driven inside the drum, water supply nozzle which supplies water in the drum, switching unit which switches on-off state of the water supply from the water supply nozzle into the drum, centrifugation sorting apparatus, where wrapping material and the fractionated organic waste are supplied to the dissolution tank by the centrifugation sorting apparatus, underground water supply pipe with which the underground water for production of the solution containing organic waste is connected to the dissolution tank, branch pipe, and strainer from which foreign material in the underground water removed is detachably provided in each branch pipe. The dissolution tank is provided with an unit for stirring the organic waste supplied to the dissolution tank. The stirring unit has a stirring blade which has blade portion formed in the front end of support arranged from the outer surface of stirring shaft penetrated and rotationally driven inside the dissolution tank. The desulfurizing apparatus and methane fermentation tank are connected through a gas feeding pipe which supplies methane gas produced by the methane fermentation tank to the desulfurizing apparatus.