NOVELTY - The system (1) has a solubilization tank (31) that is mechanically sealed from external air and is equipped with a stirring unit, a hot air generation unit, and a ventilation unit, and is provided to solubilize the sludge precipitated according to aerobic fermentation. A methane formation tank (41) mechanically sealed from external air is equipped with the stirring unit and the heat exchange unit and is provided to carry out the anaerobic methane fermentation of the solubilized sludge. The transfer apparatuses (52,53,55) are made to transfer the sludge between each tank.    USE - Dual stage methane gas production system for producing methane gas from sewage and livestock excretion.    ADVANTAGE - The resource recycling of produced sludge is stimulated without using the activated sludge method. The high degree water treatment using the raw material biomass is performed. The moisture content of raw material biomass is reduced. The processing time for the back-and-front stage fermentation is shortened. The methane gas is produced reliably. Since the raw material biomass is reversed by rotation of solubilization tank, the agitation efficiency is high. The solubilization rate is raised. Since the agitation efficiency is high similarly about a latter methane formation tank, the methane gas production rate is raised. The corrosive hydrogen sulfide generated with methane formation is suppressed.    DETAILED DESCRIPTION - coagulation-sedimentation tank (21) that coagulates-and-sediments the solid suspended matter and dissolved substance in raw material biomass with adsorption or ion exchange, and obtains the sludge. The flocculant is mixed and stirred with the raw material biomass. The coagulation-sedimentation tank, the solubilization tank, and the methane formation tank are connected in order. The flocculant is provided with the multifunctional inorganic carbide material. The additional supply of the multifunctional inorganic carbide material is carried out at the solubilization tank and the methane formation tank. A portion of sludge produced in the methane formation tank is recycled to the solubilization tank and the methane formation tank. The solubilization tank and the methane formation tank are fixed to the center fixed shaft, and the drum is supported rotatably. A dehydrator (22) is provided to spin-dry the sludge, and is made to provide the thickened sludge in the condensation sedimentation tank, and is provided to transfer the thickened sludge to the solubilization tank.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the dual stage methane gas production system.    Dual stage methane gas production system (1)    Coagulation-sedimentation tank (21)    Dehydrator (22)    Solubilization tank (31)    Methane formation tank (41)    Transfer apparatuses (52,53,55)