NOVELTY - Organic waste is decompose-treated in a fermentation tank (35), where biogas emitted from the tank is de-sulfurized and supplied to a biogas utilization installation, a portion of biogas is branched and de-sulfurized, the carbon-dioxide level of gas is measured, and the measured value is compared with a preset level.    USE - For operating a methane fermentation processing apparatus which carries out decompose-treatment of organic waste, such as garbage.    ADVANTAGE - The operating method enables appropriate and continuous control of processing load in the fermentation tank, and economical measurement of carbon-dioxide level without poisoning by hydrogen sulfide. The methane fermentation processing apparatus can be run at high load. The manufacturing cost and installation area are reduced. The introduction of anaerobic fermentation promotes volume reduction and energy recovery of organic waste.    DETAILED DESCRIPTION - Organic waste is decompose-treated by an anaerobic organism in a fermentation tank (35), to form biogas. The biogas emitted from the fermentation tank is de-sulfurized by a de-sulfurizing tower (36), and supplied to a biogas utilization installation. A portion of the emitted biogas is branched in the front stage of the de-sulfurizing tower, and the branched biogas is de-sulfurized with a de-sulfurizer (41). The carbon-dioxide level of the gas is measured, and the measured value is compared with a preset carbon-dioxide level value. When the measured value increases or decreases from the preset concentration value, the processing load in the fermentation tank is decreased or increased.    An INDEPENDENT CLAIM is included for methane fermentation processing apparatus having a fermentation tank, a de-sulfurizing tower, a biogas bypass line (40), a carbon-dioxide densitometer (42), and a control apparatus, where the biogas bypass line branches one portion of the emitted biogas in the front stage of the de-sulfurizing tower, the densitometer is provided at the later stage of the de-sulfurizer, and the control apparatus controls the decrease or increase in the processing load.    DESCRIPTION OF DRAWING(S) - The figure shows the outline systematic diagram of the methane fermentation processing apparatus. (Drawing includes non-English language text).    fermentation tank (35)    de-sulfurizing tower (36)    biogas bypass line (40)    de-sulfurizer (41)    carbon-dioxide densitometer (42)