NOVELTY - Fermentation apparatus comprises fluid biomass feed pump which supplies fluid biomass, screw transfer portion, confluence injection pump which has a transfer-pump portion which continues in a row in the screw transfer portion, circuit of the digested sludge which carries out circulation return of the digested sludge extracted out from digestion tank, and mixing unit to send out the merging liquid from the confluence injection pump in the circulation path containing the circuit and a digestion tank.    USE - The apparatus is useful for fermenting biomass for producing methane. The biomass is sewage sludge (e.g. first precipitated sludge), industrial wastewater sludge, excrement, purification tank sludge, foodstuff waste materials (e.g. organic refuse, and soybean curd residue) and livestock excrement.    ADVANTAGE - The apparatus enables to digest biomass rapidly.    DETAILED DESCRIPTION - Fermentation apparatus comprises (a) fluid biomass feed pump which supplies fluid biomass (1), screw transfer portion which makes the fluid biomass and non-fluidity biomass (2) which are supplied from the fluid biomass feed pump to merge inside, where the screw transfer portion (11) transfers the merging liquid in one direction, confluence injection pump (10) which has a transfer pump portion (12) which continues in a row in the screw transfer portion, where the confluence injection pump transfers the merging liquid quantitatively and sends it out, circuit (20) of the digested sludge which carries out circulation return of the digested sludge extracted out from digestion tank, and mixing unit (23) to send out the merging liquid from the confluence injection pump in the circulation path containing the circuit and a digestion tank, (b) fluid biomass feed pump which supplies fluid biomass, the screw transfer portion, the confluence injection pump which has a transfer-pump portion, the circuit of the digested sludge, temperature control unit (21) of a digested sludge provided in the circuit, the mixing unit, and sludge crusher (24) which carries out the crushing process of the injection liquid which is provided in the circuit and circulates through the circuit, or (c) confluence storage tank which makes fluid biomass and non-fluidity biomass to merge, the screw transfer portion, the confluence injection pump, the circuit of the digested sludge, and the mixing unit.    DESCRIPTION OF DRAWING(S) - The drawing shows schematic view of the fermentation apparatus.    Fluid biomass (1)    Non-fluidity biomass (2)    Confluence injection pump (10)    Screw transfer portion (11)    Transfer pump portion (12)    Circuit (20)    Temperature control unit (21)    Mixing unit (23)    Sludge crusher (24)